Here are some questions, you ought to ask yourself before you can start building a mobile app.
There are more questions before you can start with that.
- What platforms you plan to target? Apple iOS, Anroid, Windows Phones?
- Do you have expertise to write apps in different languages (Objective-C, Java and HTML5/XAML?
- Do you need to make your app available to download in Apple iTunes, Windows Store?
- Do you want to build and manage multiple source code? Each platform will have different project.
- Can it just be a website?
If your application does not need too much resource access, you may want to use some third-party products that can build an app (not "the real" app) that will run on all devices (mobile phones).
Being Humble is a virtue, not weakness!