Here is how it works:
Each card has several pictures on it. Any two cards in the deck have a matching picture. The goal is to be the first one to call out the name of the picture. I have modify the rules a bit for my language learners. If they spot the match, but can't remember the word they need to point to it. I then supply them with the word. It only takes a few times of supplying the word before they remember. The more you play the more they learn. Students are highly motivated because they want to be able to call out the word first!
There are several versions of this game...
Spot It! Numbers and Shapes
Spot It! Alphabet
Spot It (The original game)
Spot It Junior Animals (a favorite of my students)