OnSong comes preloaded with access to a variety of chord chart services. However, you may also store your documents on a network-connected storage service.
When the screen is first accessed, no sources have yet been added. From this screen you can tap on the + button in the upper right corner to add a new source.
If you need to add additional sources, or make changes to the list of sources, tap on the Edit button in the upper right-hand corner to enter Editing Mode.
Once you have sources in your list, you can browse their files by tapping on one in the list.