It uses a set of cards, each showing some number of symbols. Overall, there are as many symbols as cards, and each card has the same number of symbols. They key feature is that for any chosen pair of cards, there will be exactly one symbol in common, and the game is essentially a competition to find that common symbol.
It can be surprisingly difficult.
After playing, you can explore the fascinating mathematics that underlies this game via the interactive Mathematics of Dobble activity.