unfortunately it's quite common for first-time does to lose litters due to inexperience. there are lots of things you can do to help their chances though!
how long ago did she give birth? sometimes it takes a couple days for the doe's milk to come in fully. this is a survival mechanism to help ensure she doesn't get mastitis in case of losing the litter in the first few days. she may make only a tiny bit of milk - enough to keep them alive for a few days until her hormones are sure they are going to live. if it's been more than three days though, there's not much you can do unless you have another doe with a similarly aged litter to foster them to. this is why most breeders will breed an experienced doe alongside a virgin doe just in case. you can tell if a kit has eaten if its belly is fat and isn't wrinkled. a kit that hasn't eaten will be a little thin and wrinkly. there is a sticky thread at the top of this forum that has pretty good photos of what they look like.
as for the fur, you can gently pluck fur from her sides and belly to cover the kits with yourself. you could also groom her with a slicker type brush that catches the loose fur into clumps and you can give those to the babies. i have one doe that had a crazy moult in the summer and i saved the fur i brushed off of her in a jar and it proved very valuable when a doe kindled on a warm night (and didn't pull much fur because of it,) then the temperatures dropped the next day. the does don't seem to care much if the fur isn't theirs either. the kits likely dug into the nest box to try and get warmer. they can also dig to the top too if they get too warm, so i wouldn't worry about them not being able to nurse because they dug down. they're pretty good at finding mom when she comes to the box.
you can also try turning the doe over and holding a kit to her and seeing if you can get it to feed, though it's a pretty unnatural position for them both so there's various levels of success. holding the doe over the nest seems to work better, but it only really helps if she has milk. unfortunately hand-feeding rabbit kits doesn't have a high success rate, so sometimes nature just takes its course
the good news is 90% of the time the doe does much better with her second litter.
good luck!
