Welcome to the forum.
So, you have seen a girl at your college and you have fallen in love with her, without really knowing her. This may just be a crush, because you have not spoken with her or interacted with her at all.
First, you need to get to know her. This shouldn't be too difficult, if she is in your class. Talk to her about the subjects. Ask her opinion. Ask her advice on homework. Ask if she would like to work with you in the library.
Get to know other people ~ maybe you could go around together in the same group.
If and when you
do get to know her properly, then you will discover whether you really like her. If you do, then you could ask her out on a date.
