Depends on their age.
You'd need to buy KMR kitten formula. Feed them every 2-3 hours using a bottle.
If you massage their bellies, right above their genitels with a damp clothe, this should make them pee. Do this often. They won't eat if they don't pee sometimes.
If their eyes aren't open, they're probably 1-2 weeks old.
Around 4 they start to walk instead of crawl.
At 3-4 weeks they'd be interested in eating regular cat food (in this case, get either canned kitty food or dry kitten food moistened with water). Also around this age they'd be playing with each other and more responsive to stuff around them more (esp towards 4 weeks).
Also, kittens are supposed to gain a certain amount of weight per week. So you'd need to keep track of that to make sure they are eating enough. I forgot the number offhand, but you can look it up on google, Im sure.