Admins can do everything. They can create/edit employees and restrict what each employee can see/do.
Employees cannot turn features on/off, access account billing, or create/edit employees.
There can only be one Administrator per account. To change the admin, go to the employees section, and click on "Make Administrator" for the employee you wish to make the admin. In doing this, the previous admin is now an employee and cannot revert back to an admin. Only the new admin can switch back to the old admin.