cake is not directly available in app - while you are in the right folder you still need to call the cake command relative from there:
\app>.\Console\cake
Note that this syntax is unique to Windows
For UNIX use
\app>Console/cake
In case you are using an old app version or didnt bake your application with the Console folder (which you should, though), you can also call the cake core version of it relatively from the APP dir:
\app>..\lib\Cake\Console\cake
(WIN)
\app>../lib/Cake/Console/cake
(UNIX)
Either way the cake file needs to have sufficient execution rights (UNIX mainly) and PHP must be in the system env path. Then it will all work out of the box.