To build and run apps, you need to install SDKs for each platform you wish to target. Alternatively, if you are using browser for development you can use browser platform which does not require any platform SDKs.
To check if you satisfy requirements for building the platform:
$ cordova requirements
Requirements check results for android:
Java JDK: installed .
Android SDK: installed
Android target: installed android-19,android-21,android-22,android-23,Google Inc.:Google APIs:19,Google Inc.:Google APIs (x86 System Image):19,Google Inc.:Google APIs:23
Requirements check results for ios:
Apple OS X: not installed
Cordova tooling for iOS requires Apple OS X
Error: Some of requirements check failed