Such a nice person to take the kitten in.
Well.... its quite difficult for us to give you tips because we don't know how old the little thing is.
If its around one month, you will still need to give it milk.
Go to a pet shop and get 'Pet's Own Milk' and feed it with a syringe.
When feeding it put the syringe at the side of the mouth and slowly pump the milk in.
Dont do fast as you might get milk into the lungs and it will die.
If the small fella has teeth already, it can eat wet food but still need to give it milk.
Please dont buy the the cheap milk as it will only cause diarrhea in the kitten.
Good luck!