I agree with Cockney_si. I'm a singer and come from a musical family so it seems I had no choice, not that it always follows. I think half of it is to do with listening - listen to something, sing along with it, listen to yourself- are you singing the same thing?
Also important is singing with meaning - I hear a lot of singers at my studio copying the vocal acrobatics of the singers they admire. Especially that groaning thing that they do now. But they're not singing the words as if they mean them.
Singing in a choir is a great thing to do - again, you have to listen to those around you and make sure that you're not singing above them.
But yes, I'm determined that everyone can sing - even if you're tone deaf I'm sure you can find a way!
I could go on, but I won't, for now :-)
So janetsflower, find a singing teacher or coach that you like and who specialises in beginners, and have a go!