Hi and welcome to Trainz,
When you start your TS12, you will get a start-up screen with 8 options. One of them is Content. That option will take you to the "Content Manager" (also refered to as the "DLS", being the DownLoad Site which is a web version with similar functionality). In that you can download all sorts of things. If you want routes, open the search thingie on the left side, click on the + and select "Category = route". As it is for TS12, I would advice you to also add the filter "Minimum build version = 2.7", just to be on the safe side for now.
You currently should be able to find 1452 routes that way.
Good luck.
