So have you ever wanted to take your mii on the go and message your friends with tamagotchi life style like text to speech without most of the weird antics? No well Nintendo decided to do it anyways.
You can customize your Mii with coins(in game currency) which you get by answering questions. Which I have to assume is some autofill survery form. But most of the questions are personal and a few odd ones here and there stalker like questions.
There is the same level of customization with face, hair, color, and positions as the WiiU counter part of the Mii's but there is also customization with clothes, something the WiiU does not offer nor does the 3ds.
Well you can customize the box room you are in with pictures of your mii and other miis but you can't do much on that front in comparison to tamagotchi life. Pretty much just edit your mii's, add clothes, answer questions, and that is all there is to this app so far. Supposevily there are game tickets in the game but I haven't found a use for them.