Google is your friend, use it.
Soak bread in water and use a paper towel for them to suckle on until you can go out and get kitten formula and a syringe from your local pet store.
Once you get formula, its pretty easy to use. You just mix it up with warm water, put it in the syringe, hold the kitty, put the syringe in their mouth, and very carefully dribble it in while they suckle.
If she isn’t feeding them at all, you’ll need to do this every few hours.
If you can also try dribbling formula around her nipples to help guide the babies latch on. If you have a kitchen scale, try weighing them to make sure they are gaining weight. They should gain a few ounces a day I think, but look it up to be sure.
If she still isn’t feeding them and you can’t get them to eat from the syringe, contact a veterinarian for help. They can guide you through it and investigate whats upsetting her if she is have trouble feeding them.
Hope that helps!