a 3 week old puppy is too young to leave it's mother, it hasn't been weaned yet. when you are shopping for a puppy make sure that there are no visible sores, look for fleas; check the gums make sure they are nice and pint (if they are too white, the pup may be anemic).
a puppy age is week old
. Get your puppy to the vet.
A two week old puppy is blind but when its eyes open it can see.
Yes.
The puppy can get sick.
Keep it in warm conditions, lying on a blanket and keep it with it's mother.
It may have worms, you should let a vet have a look at it.
Yes you can give a 3 week old puppy milk. Because I have a 3 week old puppy and drinks it fine. So the answer is yes
No.
a puppy wormer
The puppy may be injured. Bring it to a vet.
yes.