Select the track you want to parallel, and the new parallel track will appear beside it. You control which side the new track will be on by moving the cursor from one side to the other of the selected track.
This is very useful for creating sidings and yards.
You cannot create tracks parallel to turnouts or sectional track.
It is possible to create tracks that abut (the End-Points are very close and aligned). These End-Points will be automatically connected.