There are some things you are born with and some things you can train for.
Some people can sing and some can't; this is genetic, it's about whether or not you're tone deaf. Unfortunately, if you can't sing in tune then it's not something you can learn to do.
If you can sing in tune, then if you are serious about singing it's probably a good idea to take lessons. Here, you can learn the proper breathing techniques and how to get the most out of your voice. Some of this comes with natural talent, but unlike having a musical ear this is something that you can improve by learning.
It might also be a good idea to make sure you can read and understand music (manuscript) and follow a conductor.
Take part in live shows. Join a choir, a singing group or even a drama society. Get yourself on stage and have fun!
Other than that, just make sure you practice a lot!! (which is something your singing teacher will say to you anyway)