It is wonderful that you are thinking about your yorkies oral hygiene.
Some small dogs are prone to tartar accumulation, so you are doing the right thing looking into dental care. Daily is ideal.
As for the toothpaste, the most important thing is to use a product specifically designed for dogs. You may already know this, but using human toothpaste on a dog can be dangerous.
Alot of folks here use PetzLife gel or spray. Petzlife gel is great for removing existing tartar, as well as for ongoing maintenance for their pearly whites. Some folks don't like that Petzlife contains a high amount of alcohol. But others love it because it works so amazingly well. Some folks buy poultry-flavored or peanut-butter flavored doggy toothpaste from any large petstore.
Have you tried a search yet, maybe using keyword toothpaste? This topic comes up pretty often, so I bet you will find lots of helpful info in the old threads, especially in the Health section. There are even good tips on how to get your dog used to toothbrushing, and what kinds of toothbrushes folks use.
Getting into a good dental hygiene routine should remove alot of the tartar and prevent future buildup. That alone will freshen up their breath.
A dental cleaning at the vet may also accelerate the process of removing existing tartar. This can be dangerous though because it usually involves heavy anesthesia. Alot of folks will add a dental cleaning when the pet is already going under anesthesia for another procedure, such as spaying.
Good luck! Keep us posted on how the new routine goes.