Wow, I really don't know how to talk to girls (or people in general)

I've realized just recently (26 now) that I really do not know how I'm supposed to talk to girls, or people in general.

I'm trying to get better at socializing, but it seems like one of the most difficult things I'm facing ever. I didn't really care to socialize in my childhood-teens (partially my parent's fault who raised me sheltered and discouraged me from going out, partially my fault, cause I just didn't care about socializing with others, I just was happy within my own little world) and thus I feel like I'm missing some basic or maybe intermediate social skills. I also wouldn't rule out that I'm possibly autistic, since I just don't understand some social ques and interactions, but it may be ADHD rather (will get checked out cause I do have depression).

Now, I'm not an absolute social retard, I started socializing in my later teens, and I do have social circles I regularly hang out with by now, and I push myself to go out and practice socializing, as TRP also recommends, but it feels like I'm stuck and hitting a wall and I don't know why. I've looked up some basic stuff too like the "How to win friends" book, but that only takes you so far.

The reason why I've realized I don't know how to talk to girls is cause I've hung out with a friend (who's a DJ and obviously gets pussy cause of that), and saw what how he was texting some girls. Also a girl-friend of mine (yes, I'm friendzoned by her don't know how I did it, but I don't care about her) she was showing me these text that the dude who was banging her (and whom she was madly in love with) was sending her, and I was just blown away by the shit he was coming up with, and she was just eating it all up.

I just don't know how to talk to them. It's always basic shit I get into conversations with, and my mind just blanks often (I'm pretty sure I have some degree of social anxiety too). I can't even get girls to text back nowadays (and texting for logistics has never worked). And I don't feel like I'm progressing at all, cause as I've said, I'm missing cues and shit. When I'm in conversation, it feels like I just can't process any other information other than logically what's being talked about.

And sometimes it somehow works out. I get a girl's number, maybe a kiss, maybe even a lay. But I never know how, what I did right, ect. It feels like I'm just stumbling though the interaction, and even retrospectively I don't know what I did right (or wrong).

I've honestly missed out on the memo how to interact more deeply with girls, what to say to them. What to say to them to attract them. What to say to them to get them into bed with you. When to say what. These advanced things, I've just missed out on them in my teens.

That's what I'm looking for. I learn best from example, that's why I love PUA infield footage, but I also question how legitimate they are sometimes. Also as an extra spin on all of this, this is a different culture from the US unfortunately, so there's an extra layer of difficulty since I can't get like infield footage of socializing in this small country... So anyway, any tips, resources and shit to get better at this, to even realize what to say/talk about, what's appropriate to say at what time?

Thanks!

TL;DR: I feel like only have basic social skills, and don't know how to interact more deeply with girls (and guys too), what to talk about, how to get them attracted, how to get the lay. I really want to improve, develop more advanced social skills, but I feel like I'm stuck at a huge wall.