while at the same time modifying the examples which don't apply to BlitzPlus
Most of the 2d commands are exactly the same, you've crossed the major hurdle, cos Blitz+ uses the backbuffer by default, the reason the first code worked in Blitz2D is that it uses the frontbuffer ( the screen ) by default, so the fact that you never initialised a buffer just meant you used the frontbuffer. Not in Blitz+.
I've been learning for about 9 months now, no previous experience, except a tiny bit of Pascal way back, and it is a lot of fun, Flynn, so stick with it and you will get rewards.