Is it possible to learn to sing well if you cant do it already? Or is it a natural gift that you just have to have?
If you can carry a tune you can improve. I think that 99% of people can sing. I've only met one person who was completely tone deaf (unfortunately I didn't realize this until after I dragged him into being in a musical). And it's quite possible that if I had enough time I could teach him to sing. Maybe not a Puccini aria, but enough to have fun.
Get some lessons and learn some singing exercises. They may seem dry, but exercises are so much more to help improve singing. Listen to many different styles of music and sing whenever you can. I learned a lot of stuff by singing along to the oldies station on the radio when no one else was in the car. Even if someone has a good voice to begin with there is still so much that they can learn, no one ever stops learning.
Good luck!