That means it is not on your PATH. Please see here for details on how to add Path variables.
Basically here are the steps.
- To add or edit anything environment variables in Windows 7, you need to go to System Properties first.
- Then, go to “Advanced system settings”
- Under “Advanced” tab, click on "Environment Variables …" button at bottom.
- Double click PATH and add new path into the "variable value" at the end. Make sure you separate the value with ";"
You'll want to add your platform-tools and tools directories to the PATH so you have the other tools as well.
My paths are as follows:
Platform Tools - C:\Program Files\Android\sdk\platform-tools
Tools - C:\Program Files\Android\sdk\tools
AAAPT specifically is a Build Tool, so you'll want to add that directory as well. Here's the directory:
Build Tools - C:\Program Files\Android\sdk\build-tools\18.1.0