So. You want to learn how to build a deck. There are a large number of facets I could go into, as deckbuilding is the single biggest skill in this game, but the following is as watered down an explanation as I can give.
The first and most important thing regarding deckbuilding is to understand what your deck is trying to do at all times. Whilst there are many, many decks, all of them can be lumped into these three categories. It's good to figure out what type of deck you're going for before you make it so you can fine-tune.
Aggro - Aggro decks go as fast as possible. They are known for aggressive and sacrificial plays. For an aggro deck, speed is their main goal, and they sacrifice power and denial to gain it. Aggro decks are normally beaten by midrange decks, because they simply cannot compete with higher quality creatures. Aggro decks beat control decks, because they can attack long before defenses are set up. Example decks: Doges, Monoyellow Aggro
Midrange - Midrange decks play as much quality cards as possible. For a midrange deck, overall power is their main goal, and they sacrifice speed and denial to gain it. Midrange decks can play superior cards than Aggro, but gives Control time to set up. Example decks: Caverns, Monoblue Aggro
Control - Control decks completely grind the opponent to a halt, then create an extremely hard to remove threat that wins the game. Control decks sacrifice speed and power for denial. Control decks gobble up midrange decks because they are given time to set up a board state. Aggro decks kill control decks because control needs time to set up. Example decks: Dust, Grinder Red
Note that you can combine these deck types.
These are further categories of the first three types, created in order to more easily allow players to understand what a certain type of deck is supposed to do.
Combo - Combo decks use an absurd combo to drastically improve their performance, but not instantly win the game. The simplest example is Ice/Psychosis; It used either (old) Bread Factory or Fenrier to remove the downsides of Ice, Slateskin Potion, Frozen Phoenix, Police, and Toys. Combo decks usually get destroyed if they can't produce their combo.
OTK - The control version of a combo deck, a One Turn Kill deck is a deck that seeks to perform an insane combo to instantly kill the opponent in a single turn. OTKs control the field and draw tons of cards, trying to get the combo out quickly if possible and stalling if unable to, and are unbeatable once the combo happens - You have to either heal a massive amount beforehand (usually useless) or kill the OTK deck before it happens. An old example is the Nenjas OTK. These decks are usually nerfed if they exist, as they can feel extremely cheap.
Archetype - Archetype decks are decks that use an archetype, such as doges and redcliff. Each archetype is different, but they can act the same as combo decks - disrupt the combo/archetype, the deck dies. Archetypes are like towers, you need multiple of them to actually keep the tower standing. An example is Captain Doge; it will be almost entirely useless unless there is another Doge (Archetype) card on the field.
Tempo - Tempo decks are usually aggro-oriented decks that try and maximise tempo. Tempo is an advantage obtained by playing cards efficiently and by forcing the opponent into inefficient plays. Monoblue Midrange excels at this, locking your stuff down, editing stats, and equalizing both players' boardstates.
Domination - Domination decks, also known as aggro-control decks, use a combination of denial and speedy hitters to rush you down whilst preventing you from stopping the aggro. Domination decks sacrifice power against control decks to improve their ability to deal with aggro and midrange decks. Bread is a good example, as it focuses on killing off fighters immediately and indirectly, ultimately leading to a lack of resources for the opponent to use.
Ramp - Ramp decks are midrange-oriented decks generate a ton of icons in a small amount of time, to cast huge threats far quicker than they normally can. Rainbow Midrange, Monowhite, and Caverns fall into this category.
Attrition - Attrition decks are midrange, but sometimes control decks that grind out all your resources, slowly pushing a sturdy advantage. Grinder Red gets its name from this concept, and monogreen midrange is good at it as well. Nightmares are supposed to be attrition decks.
Burn/Mill - Burn decks are decks that hit the opponent's face with effects as opposed to attacking with creatures. Mill decks use fatigue to get the same idea. The deck Burn gets its name from burn, and FR Mill gets its name from this concept.
Token - Token decks are designed to fill the field with cheap critters, then buff them to extremes. Monoyellow Aggro is a good example of such a deck.
Stallbreaker - Stallbreakers are decks designed specifically to kill control decks. Sometimes, these are control decks in their own right. Cat's Eye is a good example.
On top of this, there are also different types of cards. Here are all the types:
Starters/Lowends - These cards are very good in the earlygame, and usually cost 0 to 1 stud of a colour, as well as a low to medium amount of colourless studs.
Biggest noob mistake: People don't put enough starters in their deck, or put too many. 14 starters should give you at least 1 in your opening hand, but you shouldn't put in more than 20.
Lowends - Lowends are cards that aren't necessarily good at generating studs, but are still inexpensive. These cards are an aggro deck's best friend, as you want to play as many inexpensive things as possible if you're going fast. Examples include Glaciem Mage, a 1W2B, and Langz, a 2G.
Core - Core cards are cards that cost a medium to high amount of studs. You want the majority of your deck to be core cards, as these are stronger than starters. Midrange decks love these, aggro decks want a bit less of them. Examples include Kc666beast, a 3W4G, Mike, a 6W, and Dignity, a 2W3R.
Topends - Topends are cards that cost a ton of icons. They are called such because they are at the top end of your deck's curve. You wantno more than 5 of these usually, as these are very expensive cards and you will cry if you draw them all at once. Control decks and Midrange decks enjoy these. Aggro decks still want topends, but no more than 2-3. Examples include Regular Show, a 1W7B, PolyHex, a 5W5G, and MagikalYawn, a 3W5R.
Threats - A threat is any card that can realistically win the game. You want as many cards as possible in your deck to be threats. Aggro decks have around 30 threats whilst midrange decks have a bit closer to 26. Control decks go the complete opposite way, never using more than 7 cards to win the game.
Win Condition - Control loves being special and having its own terms. Control decks and combo decks use win conditions instead of threats. Win conditions are very hard to remove, very difficult to deal with cards that are designed to win entire games on their own if given the proper setup. As a result, you only ever need to play a small number of win conditions - Dust, the most infamous of control decks, uses only two. Examples include Eye of Heaven, Stormchaser's Gambit, and InceptionTime, though Eye of Heaven is basically impossible to base a combo deck around. Props to you if you manage to get it off.
Removal - Removal cards, such as AntiSammeh, destroy other cards or help others destroy them, like Korblox Archer. There are multiple forms of removal, and every deck wants at least a few. The Noob Mistakes article goes into a bit more detail on the types of removal.
Obviously, a card that can function as multiple of these categories is going to be very powerful. For example, AntiSammeh is both Removal and Threat.
If you want to build strong decks, this concept is vital.
Consistency is the idea that you always want your deck to be able to do the same thing every game. Card games are designed to actively make decks inconsistent, and with good reason. Inconsistency makes games fun, as the same thing won't happen twice, and it also allows weaker players with weaker decks to occasionally topple even the most powerful of decks. It is also an extremely potent balancing mechanism; if something's too powerful, an easy way to tone its power down is to make it less consistent.
In a sense, the goal of deckbuilding is to make your deck as consistent as possible. Here are a few ways of doing this:
1) Redundancy. If you play 4 two-white costing cards, you probably won't see them in your opening hand. If you play 12-14 two-white costing cards, you probably will almost always have one in your opening hand.
2) Card draw. The more cards you draw, the more likely you are to hit what you want.
3) Play Control. The longer the game goes on, the more cards you draw. Control decks sacrifice speed and versatility to make very consistent threats.