How do I limit what new users see on the admin panel?

I'm working on creating a marketplace for a specific downloadable product. I'd like my users to have their own store and upload their digital products for sale.

I entered a fake user to test the site and I see nearly the entire admin panel. I don't want my users to see most of these options, like creating categories, or choosing new themes. I want to make it simple for them, upload the file, add a description, and maybe a pdf showing a sample of the file, that's it.

I installed Easy Blogging thinking this would help, but I'm not sure if it will.