Are you a begineer? Not sure where to start? Here is a helpful documentation for you
Here, you will find resources and the learning path for Android Development.
Starting App Develpment has 3 ideas to begin with.
Native Android Development, make apps that run only in Android
Native iOS Development, make apps that run only in iOS
Cross platform, make apps that run in both devices
Each of them have pros and cons:-
Pros
Native Apps are very optimized.Since these softwares are maintained by Google and Apple themselves, in an optimum situation these apps have very small app size compared to Cross platform apps, consume less battery, better handling of background threads and more control over hardware.
Cross Platform Apps work on web technology. They work on iOS as well as Android. You will have to learn web technology to use them, by doing so you get to do both web ans well as mobile app development.
Cons
Native apps are subject to environment. If you want to make apps for Android as well as iOS wou will have to make 2 seprate apps.
Cross platform apps are not very optimized to the platform.