recoring with micro during playing

I want to use audacity for education goals.
For music player it is nice to have a rehearsal mp3 for follow/play with their music scores. In that way I want to prepare the mp3 with my spoken instructions during playing (like a letter or number, counting in the score etc).
In that way I want to record my voice in that mp3. The students get a mp3 with my instructions during listening.
How can I insert my voice (with micro) during playing that mp3?
At the moment I use 2 laptops, one with playing the mp3 and the other for narrating. After that I mix them and have reached the education goal.
I hope someone has a simple solution for this goal.

You can use the Audacity Overdubbing feature to listen to one track while you’re recording an independent second track. Normally you would use this to build a band one instrument at a time, but I bet this is right down your alley.


Thanks, that is amazing to now. Now I can go on, thanks thanks.