First post - Booking confusion

Ok...please be nice. This is my first post. We had a caravan when our boys were little, about 25yrs ago but didn’t get much experience at the time before selling up. What I do remember is that the sites we went on at the time were all grass. So improvement or not, I’m still confused with how this booking malarkey works?  I’ve been on the on line  booking site, which was fine btw, and first place I’ve booked for March (Broadway) gave me an option of hs or grass, with or without awnings, services or standard.  I’ve booked hs standard.  The second, in July, (White House Beach) only has choice of awning or not. No awnings are fully booked, I guess cos they’re on the seafront, but no choice of hs or grass for the others? According to the list Broadway has 92 hs and 4 grass and we get a choice. White House has 80 hs and 32 grass. Doesn’t make sense why we can book hs at one but not the other? Also, what happens when you turn up at the site when no one can book in till 12? Is there a long line of caravans/motor homes etc waiting their turn and it’s first in first choice? Do people that turn up on a chance get to choose before those that booked if there are places available and they’re in the queue first? I’m so sorry this has turned into such a ramble. Feel free to ignore it or dissect it and try to give me answers that I can’t seem to find in q&a.  I’ve learned such a lot from this forum already so I’ll just keep ploughing through all the other queries until I happen across ones the same as ours.