customizing user permissions in alfresco?

Am a newbie to alfresco, I am using Alfresco 3.2 Enterprise Edition. I have a task that I need to give permissions for the built in user roles. For example, Consumer can view the folder,view content, invite others and Take the ownership. I had a look at permissionDefiniti开发者_StackOverflow社区ons.xml, but still struggling in assigning persmissions. Please help me in this issue.

Thanks

• Create your own permission
• Create you own permissionGroup
• Set your permissionGroup under permissionSet type="cm:folder" tag to see you permissions once you are trying to invite a user to a folder.

Thanks