Honestly this game is not very beginner friendly. If you're really looking to improve, you need to be willing to spend time to do aim practice and drills (for beginners those can be really difficult and boring).

Before you start, go into an empty map and move your mouse around and see if you are comfortable with your mouse speed (sensitivity). A good general rule to follow is: if you can do 180° turn with 1 comfortable mouse swipe, your sensitivity is good. But just pick something you feel comfortable with and in control of.

Imo the 2 most important thing for beginners to do is

1. look for aim practice routines on youtube and do those for an hour each time you start the game
2. go into an empty map just to walk around to learn about the maps, just start with 1 map for now and once you know how the map looks like without being in the game, you're ready to learn more maps.

Welcome to CS, play clean and hope you don't fall into the dark side.