There's a few ways you can do this but this might be the easiest.
Make sure you have Snap enabled. Crop or extend the start of the track you want to copy by dragging the start of it so it "Snaps" to the closest tick on the Time Ruler. Then right click on the header of the Clip, select Copy and then Paste (Right Click > Paste) it where you want. If your project is in time and your Snap settings are correct it should just line up.
The keyboard shortcuts for Copy and Paste are the same as most other programs.
Copy = Ctrl + C
Paste = Ctrl + V
Cut = Ctrl + X
Cheers.