Very easy. Especially if it's marked "easy." Just follow the directions -- post if you get stuck, and I'll bet someone here can help you. I trace patterns too, unless I got them from a $.99 sale, in which case it's cheaper just to cut the pattern and buy another one at another sale if I ever want a different size. For interfacing, I'm guessing it's probably for a collar or placket (where the buttons/snaps go on a shirt), and if it's for the kids, you probably want "lightweight fusible interfacing." It's a big white sheet, kind of flimsy and see-through, with little dots on one side; you iron it to the pieces, and it gives them a bit of stiffness. If you go to JoAnn's or Hancock's, they usually have a big rack of various kinds near the cutting counters. Tell them what it's for, and they may be able to find you the right kind.

But seriously, give it a shot! I'm all about jumping right in with sewing -- if you really love the fabric you want to use for an item, you might consider trying the pattern first in an inexpensive fabric, so that all mistakes get made on it.