Answer:
Ummm...
Okay. Let's just assume you're young and inexperienced...
When they say a girl still has her "cherry". It means that her hymen has yet to be broken by a penis penetrating the vagina.
The hymen is usually on the very surface of the vagina, not more than a cm in, although it's important to note that not all women are born with hymen, they come in all different shapes(partially/fully covering the opening) and many hymens are torn naturally through regular activity (horse riding/tampon/even falling)