You haven't mentioned anything about what the app is supposed to do, your skill set, what tools you intend to develop the app with etc.
At the very least do some initial research, see how far you get, and then (and only then) post a specific question when you need some help.
"There are two ways of constructing a software design: One way is to make it so simple that there are obviously no deficiencies, and the other way is to make it so complicated that there are no obvious deficiencies. The first method is far more difficult." - C.A.R. Hoare