How do I take care of a baby kitten?

Just mix the cow milk with some water.It might give her a little diarrhea, but if you don't have anything else, it will be OK for just tonight. If you have some dry cat food, you can make it mushy with water and see she eats that. You said you didn't know how old she is, but she is walking around and she has teeth so she may be able to eat mushy dry food. Tomorrow, you can get some KMR at the vet or pet store and fed her according to the directions on the can.