https://support.chess.com/customer/en/portal/articles/1444777-how-do-ratings-work-
The site uses the Glicko rating formula that includes a value called the Rating Deviation (RD). When you first start, your RD is very high; that is, your rating is very uncertain. As you play games, the RD value will drop but that value will cause your rating to have large swings. The more games you play, the lower the RD goes, the lower the swings.
Why in the first games we win or lose a lot of points?