You can use your Interrail Global Pass in your own country during two travel days of your choice for one outbound trip (leaving your own country) and one inbound trip (entering your own country).
You can take as many trains as necessary to complete these journeys, but you are not allowed to make any extra trips within your own country using your Pass. You can also use them in the order you prefer (that is, you may use the inbound trip before using the outbound one if that better suits your travel plans). You can read this page for more details.