Quidditch is pronounced 'kwidich' with short vowels.
It seats 100,000 people.
To play Quidditch you have to ride on brooms.
No. Harry plays Quidditch during a cutscene, but you can't control him.
Harry plays Quidditch for Gryffindor, which is one of the Hogwarts houses.
There are three goal posts on each side of the quidditch field so there are six goal posts altogether on the quidditch field.
You need 50 quidditch cards to unlock Firebolt.
Quidditch.
Basketball.
Care to elaborate?
A direct excerpt from Quidditch through the Ages by Kennilworthy Whisp. "We owe our knowledge of the rude beginnings of Quidditch to the writings of the witch Gertie Keddle, who lived on the edge of Queerditch Marsh in the eleventh century." From this excerpt, the name for Quidditch comes directly from the name of the area it was seen to be played.
The specifics may depend on which House you're in, but officially, you need approval of the Quidditch captain(s) and your Head of House. You'll also probably have to meet some other requirements in the form of practicing (botting) and trying out, which is also a test of your botting skills. Your best bet is to ask your Prefect or your Quidditch captain. There's always people willing to help!