Can someone PLEASE tell me what exactly is a movie premiere?!

Can someone PLEASE tell me what exactly is a movie premiere?

Because i REALLY want to go to one, and i actually can, but im not sure what happens in one. I mean, sure you look at the celebrities and then they enter the movie theaters to watch the movie, but can the people there see the movie that same day too? or do they have to wait until the actual movie comes out for everybody, which is usually like a few days later......

3 weeks ago
But can a regular person just show up to a premiere early, buy tickets, and go in the theater? Or do you have to be a VIP?

cuz im dying to go to the Harry Potter 5 premiere in Chinese Theater

You can go BUT I would bet it's booked out,coz it is a premiere first public showing and that theater is one that has been selected for the actors to turn up,not all theaters are same.
Your chance of just rockin up on the off chance of a ticket at selected theater will be slim especially if Harry Potter's latest they book out months ahead♥...