I do a lot of video editing and I use Kdenlive which is both free, easy to use and for Linux, Mac and Windows so I can use it anywhere:
OpenShot is an alternative but I didn't like it as much: https://www.openshot.org/download/
I threw together a quick recording on how to do it in Kdenlive (sorry if it's a little shabby; I'm a bit busy at the moment so I couldn't spend too much time on it):
I used two chapters of the Treasure Island recordings and the cover art.
For zooming in and out you can use Ctrl+Scroll instead of using the slider; I used it for clarity.
The process is as follows:
1. Click the 'movie button' to load in the audio file/s and optionally the cover art.
2. Click the 'Continue' button when it wants to switch to a new profile.
3. Pull the audio files to the A1 channel and give a bit of spacing between the chapters.
4. Pull the cover art file to the V1 channel and make sure the length matches to the end of the last audio chapter (it will automatically snap into position when you move it to the end)
5. Click the 'Play' button (or spacebar) to check if everything seems OK.
6. Click the 'Render' button, set an output path (you can also click the little folder icon to the right of the text box) and then click MP4.
7. Finally, click the 'Render to File' button and await the rendering. It should output a file in the directory you picked. You can now upload it to YouTube!