I’ve installed it on two different comps and the multi-track recording function was not set as the default.
Go to file / preferences.
Click the Audio I/O tab and check the box marked "play other tracks while recording new one"
I’d suggest ripping the tracks into wav format. Once you’ve finished recording export and save as wav.
When burned to disk in wav format they will play on any CD player.

Load the first instrumental track into the program.
(I presume you have a microphone) click on the red record button to record your new track. The square button to stop.
If you make a mistake use ctrl+z to undo and start over.
Adjust the levels and balance with the control panels at the left of each track.
When you’re satisfied export and save as a wav file and when all your tracks are done burn them to disk.