If you have uploaded a file and would like to link to it from inside the editor, you need to know its' website address.
The website address of any file can be found by going to the File Manager.
To get to the File Manager, use the top menu and select MORE then FILES and then MANAGE
Then, navigate to the folder that contains the file and look on the far right for this icon:
Once you click the icon you will be given the address to be used to link to the file.