hello, /wsr/

i'm an undergrad and i have to make a prerecorded presentation for one of my classes. it's a five minute powerpoint presentation, but the kicker is that the lecturer wants us to record video of us presenting and have it in the corner of the presentation.
i have never done this before and don't know where to start.
i have at my disposal a laptop with a camera, a tablet and a phone. i have powerpoint, and would prefer to spend no money on any software so if you suggest something please take into consideration that it has to be free or pirateable.

how do i go about doing this? i was thinking of recording the powerpoint and recording a seperate video of my talking and then overlaying them somehow, but i don't know how my computer would go screen recording that process.

thanks in advance