I'm no scholar on Westeros history either but I believe the Targaryens came from a different continent (Valyria?) and conquered Westeros because of course they had dragons - I'm not sure how they came to have them but I think they were probably quite common where they came from. I'm not sure if George ever wrote about it and I hope someone corrects me if I'm wrong - I can't be bothered to look it up
I got through the first half of this episode before the HBO Max stream started going wonky. It was off to a good start - hopefully I can finish it today. It seems that this season will have a time jump - I see that the 2 lead actresses who's names I forget have adult versions cast. Or did that happen last night? Guess I'll find out....
Edit: So I ended up watching from the beginning today and thought it was a fantastic first episode. I'd like to see this show go on for years go through the Targaryen dynasty and end with the Mad King/Robert's Rebellion. The source material is only two books so I wonder what the plan is.....