There is only one way to invent an app. Just think about a number of applications that are currently in use right now and think about some ways to make them work better. Once you have figured this out, the rest is relatively easy.
Now creating your application requires concentration. This means you should wake up early in the morning and work on the program. In case you are not sure of what to do, you can consult an expert to help you. However, you should not give away your secrets to the guru you are consulting. You have your own ideas but you need a bit of help to perfect it. In this case, you can simply pick the brains of the expert without giving the game away.
Put on your creative hat, work hard and you will succeed. This is how to invent an app.