By changing the permissions for a role you can grant or deny users the right to perform particular actions on the website.
In the administrative menu, go to People > Permissions > Roles. Select the Roles tab, and you will see a list of all the roles that exist on the website.
Choose edit permissions for the role whose permissions you would like to change. The permissions page will show all the available actions for the website such as, for example, "post comments" or "use advanced search". The available permissions depend on the modules that are enabled in the site. Note: some permissions may have security implications, be cautious when when assigning permissions to User Roles.
Enable the permissions that you wish to grant to a particular role and disable the permissions that you wish to deny to a particular role.
Click Save permissions on top of the page to save the changes.