Modules can be enabled by going to the Role Module screen found in the Role & Rights menu in Admin module. After following the steps detailed in the role module link. Make sure you logout and login again so that the changes could be saved.  Now when you login, you can see that the module has been added.

In some instances, not all menus will be added to the module and these can be enabled by going over to Role Menu. After enabling, please logout so that the application records the changes.