Congratulations on your first Yorkie. You have come to the right place for information. If you don't get the answers that will work for you, if you use the Search function you be in potty training overload.
There are so many different ideas about potty training you have to find one that makes sense to you. Good Luck -- and if you come up with some neat little tricks that work well, please post them.
The first thing I'd do is find a very high level treat -- one that your baby would do ANYTHING to get. Use this specific treat ONLY for good potty! If you are training to go outside, I would select a spot you want Duke to use. Every time you take him outside take him to that spot and tell him to go _____. I am embarrassed to say that I started with TinkleDinkle and Poopsie.
. Any when they "do the deed" praise them like there is no tomorrow and give the treat and take immediately back inside. If you are consistent, it won't take very long before Duke will at least get the idea, but it may take several months for him to get good at it. Remember the praise and treats!