Heya,
I find most tutorials on YouTube are more advertisements than they are truly workshop. There are a few out there, but none of them are all encompassing and really just show casing equipment more than teaching. If you already know basics, you can learn from them quickly just seeing the stuff if you pay attention to placement and the way the equipment is being used. But I've yet to come across a workshop that was designed to just be a workshop and not sell something with it. But, I'm not a big youtuber, so maybe I missed some obvious good ones.
But that said, here's my experience so far (outside of simply doing it and learning from real world experience which is the #1 teacher so far for me):
1. This forum, the lighting forum specifically, is full of very welcoming and knowledgeable folks. I learned a ton about lighting from that group and now I'm giving back, so to speak, with anything that I've learned that has been a success.
2. The Strobist. It's a good starting point. The lighting forum pointed me there, I read it, then returned to the lighting forum with questions and examples, and learned much much more after understanding some basic stuff.
3. Right back to this forum, the lighting board. Other than that, google fu gives you simple diagrams for lighting patterns & names with positions so you can try different techniques, like short lighting, clam shell, etc.
The lighting forum board is mostly portrait photographers and/or still life (like product) photographers it seems. They're a great group that are willing to help. They walked me through my first speedlites, umbrellas, and through and past my portable 600ws strobe and 60" modifiers. Very welcoming group that you can learn from, give back to, and keep the cycle going.
If there's anything I've learned, the two biggest things (regarding the kind of portrait I do, which is mostly outdoor portrait in environment) is (1) get down to your elbows and (2) lighting (natural ambient, and equipment).
Very best,