I'm probably not the best person to explain it, but the number is called an ELO rating. You were given a rating when you began and matched with other players who also have a rating.
If you win, you gain rating points and if you lose you lose rating points. The amount of points you gain or lose is not the same every game, it depends on the rating of your opponent.
If your opponent has a higher rating than you and you win, you gain more points than you would if your opponent had a lower rating than you.
If your opponent has a higher rating than you and you lose, you lose fewer points that you would if your opponent has a lower rating than you.
There is a wikipedia page about ELO ratings, and you could also prompt a LLM such as ChatGPT to explain the ELO rating system in chess so that a five year old could understand it. (Note: I'm not trying to insult you, that's just what I would do if I wanted a simple explanation for something).
II
I don't understand what do the numbers we get for playing mean.
I would appreciate it if someone could explain the language please.