A small selection of tracks are distributed in the release VDrift packages. This page describes how to get some more.
List of tracks
The following cars are in the data repository of VDrift.
Click the links in the list above then click the "Download GNU Tarball" link near the bottom of the page.
Uncompress the .tar.gz file. This should create a folder with the name of the track containing files like about.txt and roads.trk. Move that folder to vdrift/data/tracks folder. Run VDrift and your new track will be ready for racing!
You can update tracks from within VDrift itself. Click "Updates" on the main menu, then "Check for updates". If any are available go to the track in the "Manage Tracks" section and click "Apply Update".