You can use any text editor or IDE you like to create your mobile games. Some people love Sublime Text 2, some like Notepad++, etc. I use Outlaw, which is the successor to Corona Project Manager, the #1 IDE for Corona SDK. Outlaw is a commercial project but has a free trial version that's perfectly suited for learning. In fact, some people use the trial version for creating commercial apps, so you can continue to use it even after you learn Corona SDK.
Grab a copy at http://OutlawGameTools.com/download/