I have used it back in the day to make my first games.
There are maybe some old forums around with some nice tutorials since that was a thing back then. blitzforum.de is a german website with a lot of german blitz ressources, but I don't know about english equivalents.
I learned it by mostly looking at the examples and being active a lot in those forums.
While it's pretty outdated, the main difference to modern game engines is probably the lack of a world editor so for every bigger project you need to build you own. You literally have just your code and that's about it. It's great for building simple games tho or learning programming in general.
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56 days ago(+1)
My Basic Programming Tutorial is still operational.
Besides teaching you how to program in BASIC (namely using BlitzBasic), there are multiple examples on there for some classic games and game types (Mario, Tetris, Asteroids, etc.).
It's still a work in progress, and always has been, but there's plenty of info on it as it is...
But anyways, check it out if you like.