If you have created a group in SharePoint 2010 and did not assign it permission at the time of creation, the following steps will allow you to add permissions.
- Site Actions >> Site Permissions
- On the ribbon, select Grant Permissions (Note: your group will not be visible in this list of groups)
- Enter your group in the Select Users box (ex: Tony_Readers)
- Click the “Check Names” button
- In Grant Permissions, select "Grant user permissions directly" and select the permission(s) you wish to grant the group.
- Click Ok
When the list refreshed, you will now see your group in the list of groups and it will have permissions.