What Are The Nuts and Bolts of Route Planning?

I want to integrate route planning into my app. But, I'm not much of a route planner myself. I have planned some basic routes but I know some of you are hard core Gaia using, waypoint setting masters.

What are practical details of how it's done? Are you panning around the map, setting waypoints here and there and building the route between those waypoints? If so, how far apart are the waypoints and how do you determine where to set them?

Or, are there tools built into the mapping app you use that build the route for you (my app does this at a basic level).