If user or group would like to view folders, reports and subscribe to reports, you can add them to Browser role.
Content Manager Role :
If user or group need to manage contents in Report Server you can add them to Content Manager Role. They will be able to manager folders, reports and other resources.
My Reports Role:
If user or group is added to this role, they will be able to publish report, create linked reports, manager folders, reports and resources in user's My Report Folder.
If we want our user/group to have publish permissions, we can add user/group to this role and they will be able to publish report and linked report to report server.
Report Builder Role:
If we have users who often need to view the definition of reports by using Report Builder, we can add those users in this role.