Kind of an involved process, but worth it in cases where I don't know the route:
- I use bikely.com to plan out the route.
- Use bikely to save the route as a GPX file to my computer.
- Garmin Edge doesn't natively read gpx files, so I use gypsies.com to convert that file into a crs or tcx file (whichever works w/your computer) & save it back to my computer.
- Use Garmin Training Center to import the course from my computer, add waypoints, and send it to my Garmin
- Using Garmin, go to menu: training: courses to start the course. It will give you alerts when you approach the coming turn, distance & time to the next turn and the finish, and a map (showing only the roads you placed into the course on bikely), and a simple altitude profile.
Like I said, rather involved, but worth it on longer rides or rides I don't know the route--I then don't have to use a paper route slip.