Hi and welcome!!
As far as critiquing, I felt intimidated when I first got here, but I just jumped in both feet and started leaving feedback on all the challenge entries (can't do it anymore, at least not all of them). You don't have to know everything to leave feedback, just know what you like as a reader
And yes, "y'all" is said here, but mostly by folks in the south, or people like me -married to a southern boy
(although I was known to say it before that, since I grew up listening to country music lol).
Best advice - aside from my quote from Cori in my sig... just write. You can't get better if you don't do it. I had a very very dry spell over the last year. But, just recently, things started to work again.