Limping in dogs is most commonly caused by a sticker or thorn in the dogs paw or due to an injury to the paw that needs time to heal.
The dog will usually lick it's paw if it had an injury to the paw to help it heal up.
Usually the limping in the dog should be over with within a week or two weeks without needing to see the Vet.
But if the dog has rested and the limping still occurs after a few weeks and doesn't go away then a vet visit would be recommended to make sure something else isn't wrong.
I wouldn't rush to the vet though if your dog has just suddenly started limping as most times a dog limping is nothing very serious and usually goes away on it's own without treatment.
Just allow your dog time to rest and check it's paws for any possible thorns, stickers or anything else that could have gotten into your dogs paws and remove it with tweezers if possible.
The dog should be feeling better within a week or two and if not and it's still limping then something could be wrong with the leg and should be checked out by the vet.
But if you can afford the vet visit and want to see what's wrong with the dog then you can still take it to the vet.