It has to introduce your main character. You don't have to go into details, but you need enough to show if the MC is male or female, old or young, and ideally, give an idea of their personality. The opening has to show, or at least hint at, the inciting incident, the problem that starts the story for the MC. Most important, your opening has to grab the reader. Very few people have the patience to wade through pages of description before the action starts. Work on the first paragraph, and particularly the first line, until no-one can resist reading on. So, a few ways to get it wrong. Fuck the main character! This too is just for narcissist nincompoops who can't read about anything but themselves.

There are fashions in writing, just as there are in clothes. The modern trend, particularly for genre or YA fiction, but increasingly in literary fiction too, is to start the story with the main character on the first page, and to start with the inciting incident. No backstory before chapter three, and then pare it to the bone. "YA" most likely stands for young adult. There hardly is a brand of monkeys that are stupider than young adults. Except YA writers. Give them a dildo and it will keep them occupied for hours.