You can use any text editor or IDE you like to create your mobile games. (You can't use a word processor!) Some people love Sublime Text 2, some like Notepad++, etc. In the following videos I use Outlaw, which is no longer available.
If you don't have a favorite, give Visual Studio Code a try. It's free and runs on Windows, Mac, and Linux. It's what I often use for coding games now.