the copilot will make it so you don't have to physically got to the nav map. you just punch in a quick series of commands (you know, you 'talk' to him/her) and they plot your course. if you have a mission, he/she'll automatically plot the course to get you to where you're going, choose the appropriate speed to get you there fastest, etc...etc, and also ensure you don't run out of gas before you get there. they do all that, so you don't have to with a simple comms like interface.
c - call up comms menu, 1 - co-pilot, 2 - plot course to - brings up nav options 3 - take over control of the ship
or something like the above, just a quick example that.
they'll also fly the ship whil you take over the guns, if you don't have any gunners.