How can some people who has a terrible singing voice practice to have a beautiful singing voice? ?

I admire your spirit. But may I ask, are you tone deaf? If you are tone deaf, it may take a while before you really get good. You must know how to hit the notes first before you can start learning dynamics, vibrato and technicalities. Try listening to yourself to hit the right notes, especially the half notes. It would help if there's someone else listening to you. Learn to hit it and you'll be fine.

I don't think that there is a way to train yourself to be a better singer. You're either born with it or not. Yes, there are way's to become a BETTER singer by taking voice lessons, but if you aren't very good now, you aren't going to be.

You might want to look into getting professional singing instructions. Check your local classified adds.

How old are you??? You could always try going into a college and looking for a singing program.

I think you can if not try acting