When you join a chess club you get rated as well. You will get a number that shows your playing strenght.
A chess rating system is used to estimate a players performance in a chess tournament or chess match. 1970 the Elo rating system replaced earlier systems as they were inaccurate. Arpad Elo developed a system based on statistical estimation assuming that the average performance of a chess player changes only slowly over time.
The Elo rating system has been refined when the computers came up. In earlier times chess ratings had to be calculated manually. There are different versions used by different organizations nowadays and only the general ideas of Elo have been adopted. This means that somebody with a FIDE rating of 2200 will have a different rating with USCF.
But any rating system is still called -the Elo system- by chess players in respect to Arpad Elo's contribution.
The Performance level is calculated from wins, losses and draws. When a player wins he has performed on a higher level than the opponent. When he loses he has performed on a lower level and a draw indicates that both players have performed on the same level.
Your rating will move up faster when you win against a player who has a higher rating than you compared to winning against somebody who plays at the same level like you.
When you have played chess for a long period of time (30 years) then your rating moves higher only very slowly when you have played better lately as usual and have made more points in tournaments.
But a young player who has played chess for only two years and getting stronger fast, has a much more flexible rating and can move higher faster if he keeps playing well.