What is squirting?

I've never done it before and I do know that it's normal not to be able to squirt not all woman have the ability to and that it can be caused by an orgasm

But what is it exactly?

What exactly does the liquid that comes out of a woman consist of?

What is the purpose behind it

And why do only certain woman have the ability to squirt?

So many questions, does anyone have any answers??? Or maybe even more questions add them in the comments please!