A dog that is throwing up could be caused by overeating or due to a stomach flu or just an upset stomach which will usually resolve itself within a day or two.
If your dog is throwing up multiple times per day or the throwing up or vomiting doesn't stop after 3 to 4 days then the dog could have some other illness that should be checked out by the vet.
I wouldn't really worry about the dog throwing up until the vomiting continues for at least 4 days and the vomiting continues to happen more than a few times per day.
But if you're worried then having the vet check the dog out can be a good idea just to be safe if you can afford the vet visit.
You can give your dog some Pepto Bismol to help them settle there stomach and it should stop the dog vomiting.