I can't stop thinking about this girl but we're not even friends and still she turns me on. How can I let her know how I feel?

In my experience the best way to let someone know that you like them is to actually talk to them. Something simple and easy at first. Invite her to a cup of coffee and just start to get to know each other. And you see how things evolve from there. Most important thing in a relationship is that you should be able to trust and have fun with your partner. If you don't get along at a humain level and you like her just for her appearance there are strong chances that the thing wont work. And again this is only my experience and my opinion it shouldn't be taken as the truth.

You can just straight forward tell her how you feel, but don't be rude, be polite and patient while you say this to her . Make sure not to make her feel uncomfortable . There are two possibilities : Either she will block you /stop talking to you or you two will be a thing :) . I definitely think its worth a try to tell her how you feel . And also, its just my personal opinion and not a straight forward advice as you know better what should be done than me myself. thank you :)