It depends on your targeted platform:
iOS: XCode (requires a MacOSX)
(
https://developer.apple.com/)
Android: IntelliJ Android Studio (free)
(
http://developer.android.com/sdk/installing/studio.html)
Windows Phone:
Visual Studio:
http://www.visualstudio.com/And then there are quite a few hybrid solutions: One Code-base -> multiple MobileOS
- Phonegap: You develop in HTML/JS and submit to
http://build.phonegap.com- QT Mobile:
http://qt-project.org/- Unity Mobile:
http://unity3d.com/ (only for games)
- CocoonJS:
https://www.ludei.com/cocoonjs/ (primarily for games)
And then there is the fees:
iOS: 100$ / year developer license to upload it to the iOS app-store
Android: once 25$ merchant fee to confirm your Google-Play-Developer Account
But those are just the tools you will need to get started, you will (very likely) need additional software.
But for each of those tools you will find hunderets of tutorials and help-sites on how to create apps, however be aware, that you won't be able to make your dream-app in a week if you don't know anything about the matter right now(expect the time to be at least half a year, unless you are full-time at it). While I encourage you to learn programming, you will have to expect a hard time if you weren't able to find help for your question on google. But I do encourage you to go that way.