Instant 100s are instant games to compete against a larger pool of players with around 100 tables. Given you're playing against a bigger field, you stand to win more points.
You're dealt deals from a previous tournament and your scores are then compared against other competitors who played in that tournament. After each board, you get to know your final score for that board and your current rank in the tournament. Do well and you'll win BBO points.
Select Instant Tournaments and then choose the instant 100 you'd like to play.
You can familiarize yourself with this format by playing the Weekly Free Instant Tournament. Once a week, on Friday morning, a new, free instant robot tournament is available to play. You can play and replay it as many times as you like. The free version does not offer points.