Yorkies should have their claws cut often as they do not have the weight to wear them down if you have never cut them go too a groomer who will do it and show you how as their claws are black , if you cut them too close your dog will never let you near them again.
The vets can do it for you or you can just tip the ends, stand the dog up on a top not on the floor and lift one foot with a good grip and snip but to be honest if the nails are long and have never been cut you need someone that can do it properly.