The 'Manage Users' feature gives others the ability to login and manage your site by creating user accounts.
To login and edit your site, the user must have a account. By
creating an account for them, or attaching your site to a user's
existing account, you give them ADMINISTRATOR access to your site.
This means that they can add and edit pages, manage the shopping cart
and orders, etc. They CANNOT view billing/credit card information or
manage users for your site.
When they login, they'll be able to see your website listed in the Site List on their Dashboard page. It will be marked with an 'A' to remind them that they are an Administrator and not the site owner.
IMPORTANT: Make sure that the person responsible
for your website subscription payment is set as the site owner and ONLY
give Administrator access to people that you trust to edit and manage