Working out if a girl is interested comes with experience, which means we all have to start somewhere.
Ask her out for something neutral, coffee, or the cinema. If she accepts, she obviously likes you as a friend but there may be nothing more in her acceptance than that.
When you have been out a couple of times, ask her to your home, or see if she asks you to hers.
If she accepts, you will start to get an impression of how she feels - friends, or something more.
The trick is, not to see something that is not there, simply because you would like it to be there!
There is one rule to remember about girls - if a girl is interested in you, she will let you know.
All you have to do is make sure that she is letting you know, and not that you wish she would, when she simply being nice.
Good luck!