The sharing feature in the WebInterface is an option you can enable in the user manager for specific folders. Just like the upload, download delete permissions, you can also add 'share'.

A shared item is by default copied to a temp location. A new random username and password is generated with a set time for when it will expire and that user and its files will be removed. You fill out an email form of the notice you want to send to the user and they will get a link giving them direct access to the files.

Enterprise users get an additional checkbox where they can share files directly between other usernames on the server. No emails are sent, the items are just made available to the user you are sharing to if that user accepts shares.

If you enable the advanced checkbox, there are a few other options that will be enabled that you can also use. The 'move' option should be used with care as the file will be removed from your own VFS and put into the temp users VFS. Your giving up control over the item. The reference will just make like a shortcut or alias to the item. You can edit the defaults for this screen.

Expiration date can be defaulted to a value such as 2 days.
To do this, in the user manager, web customizations list, go to the end of all the items.  There you will see defaults for share items.

Enterprise users have an additional option for sharing items between users. You can just enter a user's username, and they now can access the files you are sharing to them. The files will show up in a folder called "Shares" when they login.

After you have shared items, you can manage the various shared accounts you have created to lookup information on them or delete them.