the best thing to do would be to call your nearest local shelter or vet and see if they have a mother who might be able to foster them (a mother cat will provide the best care to the babies)
if you are unable to find a foster mother, here is what you do
go to your nearest shelter or vet clinic and buy some kitten formula (almost all vets carry kitten formula) kitten replacer is commonly used. It can probably be bought at a petstore, too.
Almost any brand of kitten milk replacer will work for the babies, as long as it is meant for kittens. DO NOT use puppy milk or human milk! You can also purchase a small "nipple bottle" from a petstore or vet clinic also, that you can use to feed them. Or use a small syringe or eyedropper.
Feed the kittens every 3-6 hours to begin with and as they age you can gradually start spanning the time. (6-12 hours, 12-15, twice a day, so on and so forth)
Only mix the milk replacer BEFORE you use it and serve it to them WARM, cold replacer will give them loose stools and might make them sick. If you make too much replacer, throw it out and make new the next time you feed- stale or old milk will make kittens sick.
You will have to learn to pace with the kitten- only supply AS it's drinking. If milk is coming out of its nose, you are feeding too much at once. If milk comes out, you also need to wipe it away from the nose with a warm, moist wash cloth.
I usually just fed my kittens as much as they would take, they usually decide how much to eat and when they're full. I've never had a problem with bloated kittens. They always stopped when they were full.
Feed the kitten laying down. DO NOT tip the kitten upside-down (like a baby). That can make them drown or their lungs may fill with fluids. Feed it like it would nurse from a mother, laying down on it's belly. Keep the kittens' faces clean and keep whatever you are using to feed them sanitary. Clean them in hot water after every use and in between feedings and if you are using the same device for all the kittens, make extra special sure they are clean before moving onto the next kitten.
As mentioned, you will have to stimulate these babies to pee and poop up until they are able to easily do it themselves. Use a warm, moist wash cloth, cotton ball, cotton swab, paper towel, toilet paper, napkin, ect. to gently rub the kittens' bottoms. Do not rub too hard, but do rub on their genitals for at least 2 minutes. If they don't go potty by then, then they do not need to.
Check to make sure the feces looks normal while you are stimulating them to go potty.
Keep their bottoms clean or their rears can get blocked.
Stimulate all kittens after EACH feeding.
Yes, they do need to be burped. Basically, you can lay them down on their belly (in the "nursing-from-mom" position) and pat their backs lightly. You might or might not hear a burp from them. If they don't burp, don't worry; not all kittens burp when being burped.
You will want to keep the kittens together. Keep them in a smaller box, just big enough for them to turn around and wiggle around a little bit in. Make sure it is a TALL box, so there are no chances of escape. Do not get a box with a lid, as this will not provide enough ventilation. We housed our kittens in a laundry basket.
Cover the top of the box with a light-weight sheet, to keep out the light. But make sure that there is still plenty of air circulation through it. Since their ears and eyes aren't even open yet, it will be important that light intake to their eyes is minimum so they will not have eye problems as adults.
Provide a heating pad, make sure it is covered by towels and blankets, though, so the kittens will not get burned, you need to be able to feel the heat through the bottom of the box, up to the top layer where the kittens will be laying. Provide plenty of towels for maximum comfort and make sure the general air temperature and towels stay warm. When you pick up the kittens, their bodies should be warm and not cold; if they are cold, you need to adjust the temperature so it is warmer for them.
You might also try placing plastic bottles of hot water along the sides (cover them up with towels) to provide something warm to lay against.
Keep the kittens together!
You can also place a stuffed animal in the box with them, it will act as a mother and help with comfort.