Where's its mother? If the mom ain't present, try to feed it powdered cats milk instead (KMR, Kitten Milk Replacer, available from vets and pet stores). If you will be using a syringe, be careful and don't let milk get in the bunny's nose: that's fatal.
Do not give the rabbit Similac or any human infant formula. Do not give the rabbit cow's milk, either. Only use KMR or, if the rabbit's wild (and an American species), use goat's milk.
It's not easy to hand-raise a rabbit. If you aren't experienced (which, if you're asking this question, you aren't), the bunny's chance of survival is very, very low. For the sake of the bunny, please consult with a local authority. It is probably best to give the rabbit up to an expert who can do the job properly. Look for a wildlife rehabber, or rabbit rescue group, or an experienced vet, or an animal shelter, or a government agency. See the related links/questions below for more help.
Feed it, love it, and pet it
it take a week
You could but Similac is formulated for humans. There are specific brands of puppy formula designed for canines. Petco sells a brand called Just Born which is a powdered formula. There are also recipes available on line for goat milk formulas that work very well for puppies. Bottle feeding puppies can be tricky. You need to monitor their weight daily and feed them several times per day.
lettuce?
It depends on the breed.
Have you just purchased this rabbit or has the doe weaned this baby? You don't say much. A 6 week old rabbit is probably weaned. You should not sart feeding it formula again.
To care for a 2-week-old cottontail rabbit, provide a warm and quiet environment, feed them kitten milk replacer every 3-4 hours, and gently stimulate their bottom to help them urinate and defecate. Avoid handling them too much and consult a wildlife rehabilitator for proper care guidance.
depends... did you feed it during that first week?
Every rabbit should have it's own pen. Rabbits can get pregnant when they are 4 months old but you don't want them to.
food
a milk
Rabbits that old should have alfalfa hay