Folders are used to organize and store mail. Web Messaging automatically creates a folder named "Inbox." (Web Messaging also creates a folder named "Sent" if you set "Save copy of outgoing mail in Sent folder" to Yes. Likewise, it creates a folder named "Deleted" if you set your "Deleted messages" preference to Move to Deleted folder.
You can create additional folder (or folders) as needed. For example, if you are working on a project about exotic parrots, you can create a folder named "Parrots" and place in that folder all the mail you send or receive that is related to this project.

You can also create "sub-folders" within a particular folder. For example, a folder named "Parrots" can have a sub-folder named "Tricks" and another one named "Sounds."

You can create, rename, and delete your folders. On the Account Options pulldown, select Manage my folders.