Basically, you break down items (almost every item in the game is disassem-able (yes that's a made up word (deal with it
)), get parts from disassembling, use said parts to create and build items, level up, discover and unlock new plans, keep leveling, and eventually unlock some pretty cool upgrades and items.Huge item sink which I guess is a good thing. Means a lot of items that didn't have a use or were cluttering up the GE before are now getting removed creating a more realistic and balanced supply/demand price. Also a money sink since often times it can be cheaper to buy items from stores (holy cow, they have a use again!) rather than off the GE.
You do need to have 80 Divination, Crafting, and Smithing to be able to start training Invention as it's an "elite" skill. Not all that difficult once you get the basics of it down. There's a nice little tutorial in game to help you get started and guides online to help as well.