a simple task
It’s not a simple task. You can do it live with a separate music player, a sound mixer with microphone and Audacity to record the mix. A very serious downside of live mixing is the inability to make a mistake. Once you fluff the production, it’s tons of work to fix it.
The broadcast people use a version of that. They have dedicated music players, a sound mixer to change the relative volumes between the songs and the voice, and either a recorder or direct to the transmitter.
At a place I used to work, one of the presenters came in with a completely mixed and produced show every day, It took him hours not counting the time he had to sit there during the broadcast. I asked him why he doesn’t bring the records in and I would show him how to live mix it.
It was a revelation. I’m not sure the quality of the show improved, but it reduced to a third the time he had to spend on it.
In direct answer to a part of that, there is Ducking where the music automatically lowers itself when you speak.
I used one computer, mixer and microphone. Play the music in iTunes and send it out to the mixer, and send the voice/music mix back in to Audacity for recording. That seemed to work on my computers. Play and Record are separate on most computers, although getting the sound in and out of the computer can be a challenge. Computers haven’t been production machines for a long time.
Without the mixer, it can be a problem to get the volumes right. You may not have to. Chris’s Compressor was designed to even out parts of a show that don’t match. I use it to level out a podcast so I can listen while hiking. Chris designed it so he could listen to opera in the car.
If you do get a process to work, write back and say how you did it.