Girls whats rong with me im 17 and almost 18 and never been in a relationship?

im not ugly im not good looking eather tho. i realy dont get the chance to talk to girls the only one i talk to is just a friend and she would never like me like that and then i never get to talk to meny girls beacuse im shy and i dont even know what i should do should i just walk up to some random table and say sup and sit there at lunch or what i dont realy know how to spark a converstion with girls plz help im hopeless