If you click on the 'Share Folder' command you can then share an entire folder. If you check the 'Edit Rights' checkbox then your friends will be able to edit within the folder. Within the folder they will be allowed to:
- Edit documents
- Create new documents
- Upload files into the folder
- Rename documents
- Hide documents
Granting edit rights to one or a few folders is a very powerful way to allow your friends to collaborate with you on information. It is much better than emailing files back and forth or giving them the login information to your entire account.