What kind of dog do you have? How large? How do you know for sure his leg is broken?
It is best to keep him confined in a crate or small room, like a bathroom, and do not let him put weight on the leg, if possible.
Can you splint his leg? Do you have some thin wood, or something stiff made from plastic that you can splint it with? You could wrap it with material that is soft, like a cotton undershirt cut into strips, and do not make it too tight, but enough to keep the leg from having the dog put any pressure put on it.
But, the best thing is still to find somewhere or someone to talk to that can take you to an emergency vet somewhere to have the dog's leg looked at professionally. It may even need to be operated on, depending how badly it is broken, or what size dog you have.
The links above and below have many different links about emergencies, that you may be able to bookmark and keep on hand for any emergencies with your dog.
I would really try to find some way to get help for your dog, but until you can, keep your dog quiet, and write back to this site with more information about what happened to your dog, and please answer the first questions I asked at the beginning of my post.
God bless and take care!