Start a garage band and once u get good enough, ask to perform at small places such as cafs, and little dinner places who might need a singer, or small group. And maybe one day someone famous will discover you.
YouTube is great, but you should start with the basics. doing little local competitions, school plays/ shows, auditioning for lots of things, sing at cafe's (Lady Gaga started off doing that). if you don't have a vocal teacher, (personally) i highly suggest that you get one. they are the one's that tend to have lots of connections.If you're going to do YouTube, perform songs that you wrote- not covers (just saying b/c lots of people do covers). hope this helped and good luck :)