For the first twenty games, your rating is a running average of your scores.
If you win a game, you score opponent's rating + 400.
If you lose a game, you score opponetn's rating - 400.
If you draw, you score opponent's rating.
So here's an example:
Game 1: Win v. 1600, Score 2000, Running avg. 2000.
Game 2: Loss v. 1800, Score 1400, Running avg. 1700.
Game 3: Win v. 1100, Score 1500, Running avg. 1633.
Game 4: Draw v. 1700, Score 1700, Running avg. 1650.
Game 5: Win v. 1000, Score 1400, Running avg. 1600.
Game 6: Win v. 1800, Score 2200, Running avg. 1700.
etc.
(Of course for the first 5 of your games, your rating is
artificially frozen at 1200. After 5 games, the idea is
that your provisional rating has "settled" enough to have
some meaning when displayed.)
Note that in the first 20 games, your rating can move up
or down quite a bit after each game.
After the first twenty games, your rating goes up or down
based on the standard formula, and a win never loses you
points (if your rating is so far above the rating of your
opponent, you may "win" zero points!), and a loss never
gains you points (if you lose to an RHP master, his rating
may be so high that you "lose" zero points).
After the first twenty games, the most rating points at
risk for a game is 32 points.
Hope this helps.