Each Interrail pass gives you the right to travel for two days during the validity of your pass in your home country. Most people use it to cross the border (the so called inbound/outbound days.)

There are some tests ongoing for some more days.

Use it wisely and use those days for the routes which would be the most expensive with ordinary tickets.

After using those inbound/outbound days, you need ordinary tickets to travel in your home country.

Thank you for this.

So, in theory, i could travel from berlin to hamburg and back again in a day on a Global Pass?

Yes, that is possible.