The easiest way to learn the cards is to go to the shop and buy, at least, ONE of every card.
In the beginning, you won't have any money 💰 (zenny), so just buy all the A & B level cards (they have a purple or blue outline). Next, buy the exclusive cards for the characters you like the most. Later on, you can purchase ONE of all the limited cards.
When you're ready to play, you can choose EXECUTE, tap the CARD tab, then equip.
Select SORT & FILTER, then EXCLUSIVE CARD:
The game will AUTOMATICALLY place the best cards for your selected character at the TOP of the stack.
Now you are a CARD MASTER.