To add one or several sources, pass to the "Sources" tab.
You can add sources in two ways:
1. Using the assistant.
This is the most convenient and preferable way.
More details on the assistant.
2. Using a standard form of the source settings.
Click the "Add" button in the "Sources" window:

The Source settings window will emerge:

This is where you need to enter a new source address (a web address or a hard disc path).
Consult the Source settings section for more details on the settings form.