The stray dog I care for is limping , how can I help?

There’s this stray dog I’ve been feeding and looking after for a while, and today I noticed it’s limping badly on one leg.
I can’t take it to the vet immediately. What can I do to ease its pain or treat a possible injury at home?Are there any safe ways to clean or bandage the leg? When should I know it’s urgent enough to find help?I really want to help but don’t want to make things worse.