No worries, I had to have someone tell me about the PowerPoint too lol. But it's very easy to use for drawing.
New Slide --> Blank
Then you have a bunch of shapes you can just grab, or if you want to freehand draw you can select the scribble option. The cool part of it is that you can stretch and resize and recolor EVERYTHING, including your scribbles and freeform polygons. Plus also there is an undo button. Yay!
There's also some ridiculously advanced techniques out there that allow you to chop up shapes and recolor parts of them and put them back together again...8D. You can put images in shapes, and shapes in images in shapes. It's a surprisingly powerful drawing program that almost everyone has, and they don't know about it, heh.
The tricky part is extracting the final drawing - for something simple you can just view the slideshow and printscreen it, but for art nerds that burns your drawing's resolution, in which case you should hit Select All (Ctrl + A) for your slide drawing and paste your masterpiece into paint.net or similar drawing program. Standard Paint can fail on this - if you want to be careful, edit the background in your paint program so it matches the background of the slide, or you can get a mess of ugliness or vanishing stuff.
It has its limitations - no blending modes, not really a layer system, and sometimes you have to zoom your slide to get enough drawing space for highly detailed stuff and that can mess you up...zoom in, zoom out, zoom in...but yeah. If speed is a thing and you're just trying to get that idea out of your head and into the world, it's a way to go.