I tried Pokemon Red on Advance... didn't finish it

I bought the game on eBay and have been playing it on my newly modded Gameboy Advance. IPS screen, new case & buttons. It's very nice; I'll post a picture later.

It's not explained too well on what's best to battle with. How do I know when to use an electric vs. fire without trial and error? Or is that the point?

I wonder how people figured this out before the internet was so huge.

I'm struggling to stay interested in the game. I couldn't quite figure out the purpose until later in the game... got to catch them all. But catching them all is just kinda boring to do. Maybe it's because I'm 37 and not 12 haha.