The tutorials will help. There are also some Garmin tutorials as well.
I think the best thing to do, is try and make a number of routes. I have recently planned a number of routes (10) in Germany which I gleaned from the local tourist office.
The first few, I had to sweat blood, as well as the cursing that I wanted to go back to the comfort zone of MS. After a while you get used to the creating, & amending of the routes. I am by no means an expert, but I can create a route reasonably quickly.
One of the things I like is you can store your routes (and their tracks) so you can see gaps where you have not (yet) been. However you can make nested folders so you do not have to work constantly through data you do not want.
It is a pain, but when I look back at my experiences with MS, learning that was also a pain! However I believe taking the time is worth it, and the best way is to do a real route planning otherwise it just does not work!