If your wife is breast-feeding, then for all practical purposes the baby will be attached to her a large percentage of the time. In these circumstances, the conventional wisdom for postnatal roles is: "Mommy takes care of the baby, Daddy takes care of Mommy, and hopefully someone else is there to take care of both of them." For the first few weeks, life with the kid is very challenging, but it's straightforward. All the baby will do is eat, sleep, cry, and poop. You and the wife just focus on meeting these constant demands and adjust to the fact there's a strange little person who's come to live with you. After that things start getting more complicated, and more fun.
A good book to get a perspective and ideas on caregiving for a young'un is
Your Baby and Child by Penelope Leach. It's a nice overview of what to expect from your munchkin and has useful tips and pointers. It's not aimed at Dad's in particular, but just at caregivers of a child. But even if you've got a Ward and June Cleaver arrangement going on, it's still extremely useful: both for the time you spend with the kid and to get a better picture on what your wife is dealing with all day.
Congrats, man. Don't freak out either. You'll do fine.