Maintaining User Master Records 
User master records are client-specific. You therefore need to maintain individual user master records for each client in your R/3 System.
When you maintain user master records, you assign authorization to individual users in the form of profiles. You can create a user master record in two ways.
You can create a user master record by copying an existing one. However, you can also create a completely new record and then enter the data yourself.
Authorization to Create and Maintain User Master Records Displaying, Creating and Maintaining User Master Records Copying User Master Records Displaying Profile Lists Maintaining User Defaults and Options
User Master Records and Activity Groups
Activity groups come into play if you create authorization profiles using the Profile Generator. An activity group is a collection of activities (transactions) for which you can use the Profile Generator to generate an authorization profile automatically. You then assign the activity group to the user master record as a task profile.
For further information, see the following sections:
The Profile Generator: Generating Authorization Profiles Automatically with the Profile Generator Assigning an Activity Group Comparing Profiles in the User Master Record with Activity Groups