Here's an introductory blend scene for those wishing to learn about rigid bodies!
After opening the file, hit P on the keyboard to run a simulation. Try adjusting the mass, location, and size of the "destructor" cube to learn how these settings affect the simulation.
You can also create completely new structures from the building blocks, just make sure to hold CTRL when moving them to keep them side by side. The only limit is your computer's RAM!
To save your simulation, make sure you're in the game engine and click "Game" and "Record Animation."
It took me a while to learn to use bullet physics properly, so I hope this will be of help to some and save them a bit of frustration.
Important Tips! To make your structures more stable, increase the Physics substeps to 5 (max). This will increase computational time.
Additionally, still in the Game Engine, go to the material panel and increase Friction. Default is 0.5, I usually stick it to 5 or 10. This will keep your objects from sliding around too easily. Max is 100.
To preview what some different settings do, you can view this video.