Warlock
Trade Health and cards for power while leaving yourself enough time to use it.
What the class does
Warlock's starting Hero Power spends Health to draw a card. Other Warlock cards may ask you to give something up for a strong effect. Demons and removal are common tools too.
Ask whether what you gain is worth what you pay.
Health is a limited resource
Paying Health for another card can be good when you have time and mana to use it. The same choice can lose the game if it puts you within the enemy's damage range.
A larger hand gives you choices. It does not put minions on the board by itself.
Choices to think about
Before paying Health to draw, count the enemy's board damage and likely damage from hand. Can the new card help before those attacks arrive?
If you already plan to draw, doing it before other optional plays may show you a better turn. But a whole turn spent gaining cards can leave you too far behind on the board.
Strengths and weak spots
Warlock can keep finding cards and pay unusual costs for strong effects. The challenge is to turn those cards into useful plays while keeping enough Health to survive.
See Deck Types for general game plans such as aggro, control, and combo.
The linked class guides explain the main rules and older class themes. This wiki supplies the play examples. For exact card details, use current card text and patch notes.