I thought this was extremely obvious, but I was so wrong. I looked for the town portal icon on the toolbar at the bottom, but it's not there? I checked again, no definitely not there! I checked key bindings. The T is supposed to portal me. Pressed it and nothing happened. This led me to think that this might be something I get later on in the game as there is no such thing as a Town Portal tome.
So what do I need to do to get the ability to portal back to town?