What is the best way to detect if a certain entity is colliding with the ground, where the ground is or are multiple blocks placed in the GED editor ?

For detecting collusions, use event, take a look at the manual.

Is there any more information available then : http://www.conitec.net/beta/aon_-intro.htm

Here : http://www.conitec.net/beta/aentity-event.htm

Best regards.