Mobile app development is a fast moving target. You have many options on how to develop mobile apps.
The most sophisticated way is to write native apps for each platform...
Of course you will need to master the different languages and development environments. And since you will have to develop the same functionality for several platforms, you will code it multiple times in different languages.
Happy you if you find a customer willing to pay for it.
If you wish to use the "write once run anywhere" system, then you will be landing on web apps. Fortunally today mobile devices are in most cases fast enough to run you web app without feeling slugish. So you basically can write a html 5 website and make it available as a app.
For this you can use the phonegap / cordova framework.
If you need access to some native parts of the mobile device (Sensors, camera etc.) then you can use many of the available plugins which then allows you to access these hardware specific features.
The performance of the generated code is very good, you will have a hard time to make such optimized java script code.
In this blog post serie I will guide you through the process of creating a project in netbeans, which you can then use to build your mobile application from your familiar ide.
Such apps are able to run under iOS, Android and Windows Phone. Of course platform specific features will only be available on the specific platform.
So let's start with Part 1 of the tutorial
Step 2 - Modify content
Step 3 - Build native apps