Singing is the act of producing musical sounds with the voice
A good voice is a beautiful thing. Unfortunately, I do not have a good singing voice!
It involves the use vocal rhythm and a variety of vocal techniques
You'd better tell me more about it then, as I need to learn to sing better!
A person who sings is called a singer or vocalist
That's very interesting. Are there many of these people around?
Yes. Singers perform music 
And do they write the music too, or does someone else do that?
Sometimes. Singers may perform as soloists 
I guess they are backed by an orchestra or a band. Is that correct?