Well my grandfather loves dogs.  He started giving them mush food when they
were 4 weeks old. Just take puppies food and add water in it (blend it) and mix
it well. In 8 weeks the puppies started eating regular puppy foods.

 Generally between 4-6 weeks.  At around 4 weeks I start leaving a dish of puppy kibble where the pups have access to it and mine wean themselves... But there's a lot of different approaches.
 
Do a Google search on "weaning puppies"... Then do what works for you and yours.

 Well normally dogs can use this type of food at least at the age of 1 year so that they can get variety of foods in their diet.

 My 8 week old yorkiepoo is having problems passing her bowel movement. She was doing very well adjusting to her new invireoment  I just got her a couple of days ago and she was doing well. I am feeding her the same food that she was eating with her previous owners. She gets plenty of water.  I was told to mix dry puppy food with moist food. Should i just give her the moist food instead?

 Okay well at like 4-6 weeks. Put puppy chow in a bowl and put a little warm water and blend it! After that you don't want to just put it in there and leave because it will go bad, and they wont eat it the mother would. So what you do is put some on your finger and put a little in their mouths, and keep doing this until they start to get used to it but always let them drink the milk from their mother ese them into this.