Concentration, also called Memory, tests recall. Flip two cards at a time and match pairs by rank; remember where cards hide to win.
Shuffle and lay all cards face-down in a grid.
On your turn flip two cards. If they match in rank, keep them and go again. If not, flip them back and your turn ends.
The player with the most matched pairs once all cards are collected wins.
No — you match by rank only, though some variants match by color.
Start with 20 cards (10 pairs) and add more as memory improves.