There are many different roles that members can be assigned to. Navigate to the User Roles screen in the Settings module, the link is found in the mini navigation at the top.
That page contains all the different roles, with descriptions of what each of them do. Here is the list.
If you choose Editors, then those members get an extra option to select which modules they are going to allowed to see. Click the Add a Member box and then choose a member and hit save. When they are in the list, Tap Modules next to the trash icon.
You can then toggle the modules they are able to see:
