Not as easy as writing a blog post but the tools are free to get you started. And these days, you can pretty much teach yourself how to develop apps for Android and iOS. There are loads of resources online to get your feet wet. I won’t outline them all here – instead I wanted to point you to the key programs available for download which can develop apps on Android and iOS.
For Android, meet “Android Studio“
Available for Windows, Mac and Linux.
For iOS, meet “Xcode“
Available for Mac only. There are ways around this using virtualization software.