Put all of the cards face down on a table so that nobody can see the flags and then move them around a bit, to make sure that the position of any particular flag is unknown to all players. Now each player takes it in turns to try and find a pair of flags that match.
Turn over one card at a time, ensuring that all players get the chance to see what card has been turned over. If the second card turned over matches the first, then the player removes those two cards from the playing area and puts then to one side. If the second card does not match, then both cards get turned over again and the next player has a try.
If a player successfully finds a pair, they another try and can keep going until they find two flag cards that dont match.
The winner is the player who collects the most pairs.