There are many ways to design projects in Solidworks.
The first step is to assign group members an assembly or part to design.
Least efficiently, a project will be designed part by part, and then put into an assembly. Want to change the placement of a part? If it’s attached to something, you’ll have to modify at least two parts separately. You’re free to use this method, but the other methods aren’t too hard to learn, and they will make your life so much easier.
A good design philosophy is making things parametric. Change one dimension, and multiple parts and files will auto-adjust to that change, ideally with zero errors. This is much less tedious than painstakingly modifying several parts just to change one dimension in every single one of them (often multiple times).
There are several methods of making designs parametric in Solidworks, including using layout/master sketches, but I’ll advise one popular method for now.