Depending on how you want to implement it, I find this the easiest way in RSView Studio (You can add user groups in a similar fashion):
1)In your RSView Explorer expand "System" and then expand "Users and Groups" near the bottom of the tree.
2)Right click "Users", select "New" and "User".
3)Fill in the appropriate fields for you new user and click "Create". You should see a new user in the "Users" folder in your Explorer.
4)In the Explorer, double click "User Accounts" near the top of the tree.
5)With the "User Accounts" window open, go to the top menu, click "Setup" and select "Add Users/Groups".
6)View permissions by user and click "Add".
7)Filter by "Show Users Only" and then select the user you've just added.
8)Expand "Security Codes" and you'll be able to change the relevant access levels.
You can do a whole lot more including adding groups and linking Windows accounts, but hopefully this is enough to get your started.