Well, it is complicated.
1. Make peanut butter. This involves buying peanuts, shelling them, roasting them, grinding them, adding a bit of oil and salt as necessary, and grinding a bit more.
2. Make jelly. Cook fruit in a bit of water until it becomes mushy. Run through a food mill, then cook some more. Run through a strainer (skip this if you want to make jam). Add about the same amount of sugar as you added fruit (i.e. 4 cups of chopped strawberries = 4 cup sugar). Add enough gelatine to get the right consistancy, and refrigerate (or preserve by canning).
3. Make bread. Add yeast to warm water until foamy. Add to flour (and other seeds and grains) as directed by your favorite bread recipe. Allow to rise. Punch down. Allow to rise again and then bake. Please follow bread-baking instructions if you haven't done this before.
Allow the bread to cool. Slice into slices appropriate for sandwiches.
4. Assemble peanut butter and jelly sandwich. Spread a nice layer of peanut butter on one slice of bread. Depending on your preferences, spread a layer of jelly on top of the peanut butter or on the other piece of bread. Place slices together, non-condiment-side out.
5. Cut in half if you want. Enjoy your homemade PB&J!