Welcome to YT, Kim and congratulations on your new Yorkie baby! I can assure you, this will be a whole new experience!
These little darlings
are runners! My husband found a wonderful trainer for Toto after she nearly gave us a heart attack running! When she is on the leash, he taught us to just remind her of the command "Stay with me" to keep her on the left and at our side. We were visiting friends on Thanksgiving [they live on about 40 acres] and I took Toto outside without her leash. She would kinda wander out of her designated area while sniffing and exploring! I was fine as long as I felt I could safely catch her .... then I looked over and she was out too far! I called to her and when she looked, I simply said "Stay with me" and she came running back!! WOW ... what a heartstopping moment!

The most important thing with these little ones outside is predators ... our vet constantly reminds us to be very careful of large birds of prey and coyotes, etc. We have to constantly be on our guard to protect them.
Toto is pad trained ... but she will also go outside! It just kinda happened so when she does it, we praise her just like we do when she goes on the pad! It doesn't appear to confuse her ... I suppose "when you gotta go, you gotta go!"
Looking forward to seeing pics and hearing all about your Yorkie baby!!