All routes start at a place.  Use the map to locate the start of the route you are adding.  If a place already exists at that location (a symbol is shown on the map there) then select it using the  icon and clicking on the place on the map.  Then click the tick  to confirm your choice. 

If the start location does not yet exist as a place (there is no symbol there on the map), then click the green plus  to create it.  See the help on adding a place for more information. 

A route can consist of many segments.  If your route passes intermediate places (huts, major track junctions, etc) on the way, consider breaking it down and ending the first route segment at that location, then adding further route segments for the rest of the route.

Repeat the steps used to create the start place to select / create the next place on your route - the location where the section of the route you are about to describe ends.

See help on adding route segments for more information. 

The most important route guide information is actually in the 'description' and the 'route points' of a route segment

Once you have created the first segment and saved it, you will be prompted to select / create the next place on your route (scroll to the bottom of the screen to see this).  If you have more sections of your route to add, go back to step 2 (above) and keep adding route segments until your entire route is described.  When you've finished and saved all your sections you can simply navigate away from the page.