Fast forward 20 or 30 years and what you’ll regret most are the chances you didn’t take. Therefore, if you really like this guy, let him know. The worst that could happen is he doesn’t feel the same. If that occurs, it’s no big deal. At least you can quit pining away for him.
If your crush doesn’t know you exist, then you need to make it your mission to change that by entering his social orbit. Get yourself introduced to him by a friend of his, join clubs he is involved in, sit closer to him in class, etc. Make eye contact, smile, ask him to help you with something minor, and look for excuses to initiate conversation. Asking questions is good because it often gets the other person talking about themselves. People love to talk about themselves, plus you’ll learn more about him. As you interact with him, gauge his reactions verbally and nonverbally to determine whether he shares your interest. This how you get things started with him.