Why on earth did they give away a kitten at just under 3 weeks old?
It should still have been with it's mother - unless the mother died? However that aside you can start trying to wean the kitten around the 4 week mark - everyone has different ways so you will need to try them to see which ones the kitten prefers.
You could buy a box of (human!) baby rice and make a very small saucer up of this - use the kitten milk/water for a couple of days and then try to introduce kitten food.
You can try to wean the kit off with the Whiskas/Feliex kitten food, well mushed up. If the kit doesn't seem interested you could mix some of the KMR milk in with this for the first day or two.
You could try a little cooked white fish/chicken (again finely chopped/mushed) again try a little of the milk over it for the first couple of days.
You may need to encourage the kit by putting your finger in the food and letting him lick it off type of thing or just smear a little around his mouth so he gets a taste.
You can also try Royal Canin Babycat dry - but would suggest when introducing the kit to this you perhaps add a little cooled (boiled) water over the biscuits to soften them.
Good luck. Do post a photo of the kit
