I use Map Create to do all that. The only way I know how doing it directly in the unit is to use your cursor and move it around until you have the exact coordinates of the first point. Push enter to save that point, then go to the next until you have them all in. When done save that as a route. You may have to cahnge the coordinate's format in the unit to match the format you are working with. Seems like there should be an online program to work with that.
Fair Winds and Following Seas
Bill H. PTC USN Ret
Chesapeake, Va