Basic video editing

[pink grapefruit]

Tech stuff makes me angry because I don't understand it immediately and I'm just such a shit person generally.

I have 2 .mkv files that I would like to turn into one single video file. Then, I would somehow like to record over that video (with reduced volume but maintaining original audio) with another audio recording like as I watch the video over.

They're pvp fights I was in, and I want to do like commentary about what happened, what I did wrong, etc. What software should I use for this? Just knowing what software to use would help me a lot, because then I could watch youtube videos about how to use the software.

Thanks! Hoping this isn't a super annoying request.