The user management of the MongoDB is not part of the Community Edition of Mongo Management Studio.
MongoDB has an integrated user management. This allows you to control the access to the databases and to assign read/write permissions.
In Mongo Management Studio you get access to the user management with tight-clicking on a database name in the left navigation tree and selecting "User Management" from the opened context menu. A popup with a list of existing users of the database opens and gives the option to edit or delete them. By clicking on "Add user" a form for a new user appears. A user always gets a username and a password or a usersource . In the list of the roles you can select the required one and click on the "Save" button to save the user.
A special case is the admin database, which exists in every MongoDB server instance. There are specific roles, which are only effective, if they are awarded on the admin database. To get access to the user management of admin database click with the right mouse button on the server connection and select the entry "Usermanagement" in the context menu.
If the server is running in authentication mode and still no global user exists, it comes to a "Auth failed" - error message after adding a user. In this case it must be re-connected just with the stored user data.
The user management refers to the User roles in MongoDB 2.4