You can create different user accounts to sign into the backend. Hooks are in place for plugins to develop user management. Different users can be granted different access and editing rights.
If you want to create & use multiple users, you need to do so with a plugin or manually.
There is a multiuser plugin now available in Extend: http://get-simple.info/extend/plugin/multi-user/133/ If you have installed the multi-user-plugin, you will find the user-management-tab in the right sidebar of the settings-page, “User Management”.
If you need to create a user manually, you can follow these steps:
<USR>element within that new XML file to have the same unique username created in step #2