You get 3 each turn, with some chapters giving you the ability to redraw 3, or the Best ones, Draw 6, giving you plenty of tactical options. (But you discard the ones you have, so make sure to use them first)
1) On the top right of the Card it shows how long the card effects last.
Arrow down = INSTANT (Some cards have these that last till your next turn shown on the card detail)
Hourglass 1 = Until the end of your Turn
Hourglass 2 = Until your next Turn
Hourglass — = Last until an action is taken.
Lets say you have a card that says next shot or melee is a success, if it shows Hourglass 1 it means if your turn ends and you havent killed anything? That Card buff goes…puff.
2) Top left Shows CP (Command Points) Cost, they usually go from 1-4, you get 1 CP at the start of your turn, and can use certain cards that give you Extra for each Genestealer you kill. So best use those when about to kill alot of Genes.
3) Convert, currently in need of a buff in my opinion, converting a Card gives you AP (Action Points) that the whole squad can draw from. The better the card, the more AP you get. Use this early on when you are low on CP to give your termies that extra push.
You should always be converting a card every turn (unless you are saving it) you can only convert 1 card per turn. And remember, when on overwatch, this Squad AP will help them unjam their weapons if they themselves have no AP.