The Users and Principals  dialog provides a general overview of logins, roles, users, and schemas at either Instance Level or Database Level. 

Accessing the Users and Principals view.

There are two ways to access the Users and Principals view. 

From the Instance Summary section

• Go to the instance summary section.
• Select an instance.
• On the Instance Summary panel, click View Instance Principals. This opens the Users and Principals dialog at the instance level view. 

From the Database dialog

• Go to the instance summary section.
• Select an instance.
• Go to the Databases section and select a database
• Click View Database Principals under the Security Information Section. This opens the Users and Principals dialog at the database level view.

For more details on the available information on each views refer to these documents: