iTunes "Apps" section - clarification
Question 1 answer;


To delete an app, simply go to the iTunes sidebar, and find where it 
says 'Apps'.
Click the apps window, and it will load a list of all the
applications that are stored of your computer.
Now the next step is to do a quick search for 'angry gran', in the
search field, in the top right of the window.
When you have found the offending app, click on it once, highlighting
it.
Press delete. (It will then say, 'Remove from library?'. Click yes,
and when it asks, click once again to move the app to the trash.)


Question 2 answer;

The section of the screen you have labeled in 4, is used for syncing documents, and other user created items, on, and off your iDevice. It can be used to transfer files from the iOS version of garageband, to the desktop version, vice versa. (It is in no way limited to just garageband. Many apps use this feature)

This feature only works for documents of the specific filetype for the app. If you are trying to put photos into an app, you will have to sync them normally, and then access them through the (usually) built in media browser.