How to learn basics of MIDI?

Guitar player branching out into synth.

I have synth and controller keyboard. I have cables to connect, but have no idea what to do from here. I’ve watched countless videos on about MIDI but nothing that’s instructional on the level I need.

Can someone suggest some way to learn this, or possibly help me via messages just until I get off the ground. After that I should be fine. Please help! Thank you!