Blinds are used in games such as Texas hold’em. The small blind is posted by the player directly left of the dealer button and the big blind by the next player, usually double the small blind. They post before seeing their cards, which is why they are called blind. The button moves one seat each hand, so everyone pays the blinds in turn. In tournaments, the blinds rise on a schedule, which forces players to keep playing hands.
Example
In a game with blinds of 1 and 2, the small blind puts in 1 unit and the big blind puts in 2 units. Everyone else must call 2 or more to play the hand.