Begin by creating or importing multiple 3D objects to arrange.
Select all objects you wish to arrange
Start a new Interactive Physics Session by pressing 'Physics > Interactive Physics Editor > New Interactive Physics Session' in the 3D view toolbar
Select all objects you wish to keep static (but still cause collisions)
Press the 'Physics > Make Passive' button
Now select an object and transform it – notice how other objects in the scene dynamically move out of the way
Note that the object you're moving will pass through passive (static) objects, as collisions cannot be detected while transforming an object.
If you don't like any single transformation, drop it using 'Right Click' instead of 'Left Click'.
Use the lock location/rotation axes check boxes to limit how the objects move on collision
Adjust the margin of collision between objects with the 'Physics > Collision Margin' slider
Once your Interactive Physics Session is finished, press the 'RETURN' key to commit your changes
Press the 'ESC' key to cancel your Interactive Physics Session at any time, and the objects will return to their original locations.
Installation (credit: CG Cookie):
You can download the Interactive Physics Editor from your account dashboard on the Blender Market, assuming you’ve already purchased it.
The easiest way to install the Interactive Physics Editor is to do so directly from Blender. You can do this by going to File > User Preferences > Add-ons > Install from File. This will open a File Browser in Blender, allowing to you navigate to and select the .zip file you downloaded. Press Install from file.
If your browser auto-extracted the downloaded .zip file then you will need to re-compress the Interactive Physics Editor folder before installing.
Once installed, Blender should automatically filter the addons list to show only the Interactive Physics Editor. You can then enable the add-on by clicking the checkbox on the upper right of the add-on panel.