Where do you start?
There are many possible routes and the ones most people associate with the music industry involve long-winded and/or costly processes like getting a demo recorded, going to venues and waiting for them to phone back and ask to hear more stuff before finally being approved.
The problem with that comes when you've never been on stage and have no gig history, nobody backing you up and no guarantee of a fanbase turning up.
There are several youth music charities and organizations that can get you onstage through songwriting workshops. This is one way, but they usually have age limits, and focus on collaborations with other participants while you might want to play solo or perform with people that aren't eligible due to age etc.
The way I got into commercial performance was through open-mic nights.
All you'll need to do (unless you live out in the Styx), is type your city and 'open-mic' into Google and plenty will come up. They sometimes cost but very rarely for performers. Usually if you turn up and ask the host to put your name down, you'll be given around 2-3 songs or 10 minutes (or less if you'd prefer).
Through open-mics, I have met several contacts involved in hiring me for performances. Then through these people I have met plenty of others. I've also met musicians, which I have jammed/collaborated with, (both spontaneously on the night and afterward), and even a puppeteer who hired me for live beatboxing as part of the sound design for a few shows. I have also met tons of friends and fans.
A word of warning. If you are serious about a career in the music industry, acknowledge the downside to open-mics. You are giving away a performance for free. I am happy with my performance now and I would currently only do open-mic nights to sell tickets/CDs/DVDs (about which, the venues are generally fine) or to test out new material. I used to do six a week (often two a night) and it worked wonders for my routines but everyone knew that they could see me for free. Therefore it would be best to only do them once in a while when you get to the stage of having your own gigs. Also, there are so many that it's possible to do them in a rota so that you only do each venue once a month (in most cities).
Make sure that you talk to everyone that can help you on the night. Find out if there are any promoters, ask who is in charge of bookings for the venue you're in. Speak to all the other musicians who liked your performance about their gigs and whether they need other acts.
Make sure you say your name clearly onstage along with any upcoming gigs.
Remember, the standard varies across the night; some acts may be amazing and some may be awful so don't worry about your level. You're practicing performance whilst entertaining the crowd for free.
Finally, it may seem obvious but don't bug the host. S/he will be pretty busy sorting out an evenings worth of entertainment from so many acts, including, in most cases, setting levels. Wait till they're free to ask them questions. The end of the night is the best time to ask about anything other than that night's performance.