There is no difference between a wedding cake and a regular cake, except in the stacking and decorating of it. The insides are the same as any other cake. Once you pick a flavor and a filling and/or icing, you're set. If you want a 3-layer cake you have two options for making it. you can:
A) pour all of the batter into one deep cake pan and after it cools you saw off the top to make it level and then torte it (cut it into 3 even-sized layers).
B) use 3 seperate cake pans and divide the batter among them. After they cool de-pan them and level the tops.
To assemble the cake place one of the layers leveled side down. spread filling/icing on top, leaving an inch around the edge unfrosted. And another layer, repeat filling/icing. For the final layer, place it bottom side up, so the top of the cake is absolutely flat and even. Now spead a thin layer of frosting all over the cake- this is a crumb coat. Chill the cake for 20-30 minutes. Add the rest of the frosting to the cake. You'll want an offset spatula for this. if you plan to add fondant, keep the outer frosting layer thinner than normal.
Does that help?