Finishers

A finisher is a card that ends the game or puts you so far ahead that the outcome is decided. Beginners often build decks that generate value and establish boards but never actually close games. You need 7-10 cards whose explicit job is to kill opponents.

Combat finishers

Cards that make your creatures deal lethal damage.

Craterhoof Behemoth — 8 mana, gives all your creatures +X/+X where X is your creature count, plus trample. One of the most played green finishers. In a token deck, this wins the game the turn it enters.
Triumph of the Hordes — 4 mana, gives all your creatures +1/+1, trample, and infect. 10 infect damage kills a player. A wide board with this kills the table.
Overwhelming Stampede — 5 mana, all your creatures get +X/+X where X is your greatest power, plus trample.
Extra combat steps — Aggravated Assault, Aurelia the Warleader, Savage Ventmaw + Aggravated Assault (infinite combats with enough mana).

Drain effects

Cards that drain life from all opponents simultaneously. These bypass combat entirely.

Torment of Hailfire — X spell. Each opponent repeats X times: sacrifice a nonland permanent, discard a card, or lose 3 life. At X=10+, this usually kills the table.
Exsanguinate — X spell. Each opponent loses X life, you gain that much. Simpler than Torment of Hailfire but effective.
Gray Merchant of Asphodel — creature, drains life equal to your black devotion from each opponent. Strong in mono-black and heavy-black decks, especially with recursion.

Combos

Specific card combinations that win outright.

Thassa's Oracle + Demonic Consultation — name a card not in your deck, exile your library, Thassa's Oracle triggers, you win. Two cards, compact, hard to stop.
Kiki-Jiki + Zealous Conscripts — copy Conscripts, untap Kiki-Jiki, repeat for infinite hasty tokens.
Mikaeus the Unhallowed + Triskelion — Triskelion deals damage, dies, returns with undying, repeat.

Combos need redundancy. Don't build your entire win condition around two specific cards with no backup. Run tutors or alternative combo lines.

Alternate win conditions

Cards that win the game through non-damage means.

Revel in Riches — if you have 10 Treasure tokens at your upkeep, you win. Creates Treasures when opponents' creatures die.
Approach of the Second Sun — cast it, it goes seven cards from the top. Cast it again, you win. Slow but inevitable.
Laboratory Maniac / Jace, Wielder of Mysteries — you win when you draw from an empty library. Requires self-mill or mass draw to set up.

Matching finishers to your strategy

Your win conditions should align with what your deck does naturally:

Tokens: Craterhoof, Triumph of the Hordes (you have the bodies already)
Aristocrats: Blood Artist loops, Gray Merchant (your engine is the win condition)
Control: Torment of Hailfire, combo (you have mana and cards, you need to convert them)
Voltron: Commander damage with evasion (your commander IS the finisher)
Spellslinger: Storm lines, Grapeshot, Aetherflux Reservoir

If you can't name 5 cards in your deck that kill opponents, add more.