Hello, I am sorry no one picked up your question earlier. i am not sure if you still need help with this or not, but I will answer going on the limited information you gave. Vomiting can be due to anything, from a virus that will end in 48 hours to an obstruction of the bowel, to a food change.
If the dog is still eating and drinking then you may be looking at a limited virus or a sudden dog food change. In which case you can fast the dog for 24 hours, then begin a bland diet of boiled chicken and cooked white rice. give a small amount to start and wait to see if he holds it down. If he does you can give him some more.
If it is acid like fluid then the dog may have acid reflux.
To help settle the stomach for either of the above you can try some pepcid AC. You can find dosing here. http://www.veterinaryplace.com/dog-medicine/famotidine-for-dogs/
When vet care is needed:
If the dog eats any non food items such as grass, toys, bones, greenies, rawhides etc. then you may be looking at a blockage of the bowel which needs your vet attention.
If the dog eats any fatty human foods such as steak , ham, gravy etc. then you may be looking at pancreatitis .
If the dog could have gotten into anything toxic this would cause vomiting.
If the dog got into garbage then that can cause garbage toxicosis .
I would suggest you take the vital signs to know if it is an emergency and this link goes over how to do this.
Obstruction (foreign body)
Garbage gut http://www.petplace.com/dogs/garbage-toxicosis-garbage-gut/page1.aspx