Figma has a desktop app as well. Download it from their site - it is free, after all. You only need to set up an account! You do need to be online to log in.
There is much more to teams and collaboration in Figma than what I could explain here in a few lines of text. In a nutshell: you can have as many "personal drafts" as you like. Those can be shared with others as well - but only you can work on them.
To enable collaboration, you must set up a team and invite members. Each team works with projects. Drafts can be moved to a particular team project, and team members can then work together on that file.
The free version limits this last part to three teams and only three design files and figjam files. There are other limitations: for example, team libraries (shared libraries of reusable components) are unavailable in the free version.
And the biggie is that you cannot have private projects - which means that when you share a prototype with a client, that client also gains access to your design files and may copy those to their own Figma files.
Not something that you'd want in many commercial contexts, of course.
So if you are serious about Figma and creating prototypes/design files for use in commercial work, it is strongly suggested to avoid using the free tier.
But seriously: just create a free account, download the desktop app, and try it out for yourself. The limitations of the free version are clearly spelled out on the pricing page:
Compare plans across both Figma and FigJam. Explore features (including Dev Mode), pricing and frequently asked questions.
www.figma.com