One of the most important and entertaining parts of Fallout Shelter the actual construction of the shelter. You need to build all sorts of rooms in order for the shelter to function and prosper. An energy generator and a handful of elevators are essential, but you'll also need bedrooms, coffee shops, gun stores, laboratories, and even a Nuka Cola factory.
To build all these rooms and improve your shelter, you need raw materials. However, the best resource you have are the inhabitants of the refuge. You can let in lots of people and use them for their unique abilities and attributes. In fact, as you progress, you can give them weapons and send them out into the wilderness to explore.