Unfortunately, learning how to make signatures professionally always comes at a cost.
Asking anyone here, will most likely cost you if you're looking to learn everything, same for real life private courses and online 1-1 help.
School is free I think.
If you were to teach yourself through google and youtube, you might miss some key features due to the fact you're kind of making a jiggsaw puzzle with learning this, except you'll be missing pieces if you learn yourself.
EDIT:
I do some signatures for people and stuff, and I used to do it more often in my old community. The owner of that was a full time GFX Artist, and did it for a job. He gave me some lessons for free though. Here's some of my really, crappy work.