If you want extra credit, though, here's a lil' frosting crash course. The outside of the cake will typically come in any of three types of frosting: American buttercream, Italian meringue buttercream, and fondant.
American buttercream: This is probably the kind you encounter most — it's sweeter, made with sugar, butter, and milk, and has more of that birthday cake–frosting consistency. It's a little more difficult to apply because of its thickness but can lend itself to beautiful textures; it can also generally get a smooth finish if that's what you're looking for. It's definitely the one to pick if you have a "sweet tooth" (or if, like me, all of your teeth are sweet).
Italian meringue buttercream: It's lighter, fluffier, and less sweet than American buttercream. It's also smoother to work with and lends itself to a shinier finish. That said, it's a little more fickle when it comes to holding up against the weather — in warmer temperatures it will get a little melty, so definitely consider that factor if you're planning a summer wedding.
Fondant: This is a firm sugar icing that people have a LOT of opinions about, since it doesn't have the texture of typical cake frostings. That said, it looks beautifully polished on a wedding cake and makes it a lot easier to add other design elements. If you're opting for a colorful wedding cake, this might be your best bet, too — it won't dye guests' mouths as drastically as a strong color would with typical buttercreams. (Also, if you're on Team Never Fondant because of the taste, keep an open mind — as I mentioned, people aren't really going to be tasting much of the outside of the cake.)
The choice of one of these is totally about personal preference and what you'll need to accommodate your design. That said, scatter my remains into the ocean with a vat of American buttercream, ashes to ashes, frosting to dust.
(You can check out Fluffy Thoughts' wedding cake gallery for more info/inspo!)