Aliases are pointers to real documents that you may use to distribute the same content in different folders with different security policies, you may have more than one alias that point to the same real document.
Creating an Alias
From the list of documents to select the document you want to create an alias and then choose the Copy context menu item. This will put the current selection in the clipboard.
Now in the folders tree, right-click on the destination folder an select the Paste as alias item.
The alias appears as a normal document, and you can perform on it all the operations allowed in the folder.
All the operations performed on this alias will be executed on the original document
All the modifications done on the real document will propagated to all the aliases
Aliases don't cause increases in the size of storage
Deleting an Alias
Just right-click on the alias and choose Delete. This deletes the alias only, not the real document.