Setting up Security Roles is a very important step in configuring your CRM. It's also very complicated and usually an iterative process. As the months go by, it's easy to forget which users have been assigned which roles. If you are not a System Administrator, you may not even know what Security Role(s) have been assigned to you! You can, of course, go to the User record and click Manage Roles to view each user's Security Role(s), this can be tedious if you need to check multiple Users.
Fortunately, there's an out of the box report called the User Summary which can help you sort things out- and you don't have to be a System Administrator to run it.
Step 1: Navigate to Settings==>Administration==>Users
Step 2: Click "Run Reports" and select User Summary
Step 3: Select All Applicable records and click "Run Report"
The report shows each user in CRM and the Security Role(s) assigned to them