What are ratings?
Ratings attempt to measure a user's current chess playing strength. The higher someone's rating is, the harder they are to beat. Playing opponents near your rating should result in a competitive game.
The rating system used at Chesspark is the Glicko system, which is similar to the Elo system and to the systems used by the USCF and FIDE. One addition of the Glicko system is the Rating Deviation (RD) which is a measure of how certain a user's rating is. A person whose RD is 350 has a very uncertain rating, and a person whose RD is 30 has a rating the system is pretty confident about.
A user's rating changes after each rated game played. In general it will move upward when the user wins and downward when they lose. A drawn game will make the rating move up if the opponent had a higher rating and down if the opponent had a lower rating. The amount of the rating change is greater if the user's RD is larger, and less if it is small. The RD value will get smaller as you play more games, and larger if you go for long periods of times without playing.
How do you calculate my rating?
There are 2 parts to your rating. A rating and the rating deviation (RD). Putting these together forms a confidence interval (from statistics). So really player's real strength is very likely to be between rating - RD and rating + RD. The smaller RD is, the more confidence the system has in your rating. The Glicko formula is applied using the two users' ratings, RDs, and the score of the game to come up with a new rating for both players. One difference from the USCF rating system is that rating points are not conserved.
How do I improve my rating?
The most efficient way to improve your rating is to beat higher rated players. Try playing users close to, but higher than your own rating.