They have a team helping them prepare called seconds, they also keep aware of opening updates by following games around the world. They have large opening datab

They have a team helping them prepare called seconds, they also keep aware of opening updates by following games around the world. They have large opening databases, and will use computers to find new moves (originally just a team of GMs) known as "novelties" (a surprise). The novelties take the opponent "out of book" or the prep (preparation) he has developed. This means the opponent will have to use more time, and find his way out of a tricky situation you are more familiar with, through computer analysis. Often old sidelines will come back into fashion in order to avoid prep, or to lead someone into unfamiliar territory. If you watch on a video feed, announcers will sometimes say "this position was played in city (x) in year (n) between player(1) and player(2)" this is to show that there are few games left in the database, we are entering deep prep. Hope I helped.