Start by clicking on the Create a New Adventure button on the bottom left hand side of the screen.
Select the Draw a Route option and begin by clicking on screen where you would like to start your route.
You will see you can now move your cursor to create the route and click to place the next point.
You can select the SnapTo option on the top of the screen, allowing the route to stick very easily to existing trails on the map.
If you prefer to draw your line freely, deselect the SnapTo option to turn it off.
To finish the route, simply hit the Enter/Return key and you will see a finishing flag marking the end.