The Go Back command moves the insertion point to its previous location. Source Insight keeps a selection history, which is a circular list of the last 100 positions you've visited. The selection history is global to all open files, not just the current file.
The Go Back and Go Forward commands function like the navigation buttons in a web browser.
The Go Back command works nicely with the Jump To Definition command. If you jump to a function definition, you can use Go Back to go back to the function caller. This process can recurse many times. You can use Go Back, and Go Forward to traverse the call chain forward and backward.
The selection history is circular, so eventually you will end up at your starting point.
You can use the Selection History command to show the list. That command shows each position, along with the function or enclosing symbol at each location.