How do you fast travel? What buttons do I use to fast travel? Thanks

You have to have found more than a couple locations, first. Then you open the pipboy map, highlight the travel location you want to go to, and double click. You can't fast travel somewhere until you've discovered/found it.

The easiest way to fast travel is this: first you have to have been to several locations. Second thing is you go into your pipboy. Third thing is you go to the map tab. Fourth thing is you move your cursor over the location you want to fast travel to. Finally you select location and there you have it.