It goes into detail about how the ground lead on the probes is ground and the fact that you have to pay attention to where you are connecting them otherwise you can create a short circuit. Note that all the probe grounds are connected together, so connecting two ground leads to two different circuit nodes effectively shorts those two nodes together.
EEVblog #279 - How NOT To Blow Up Your Oscilloscope!
https://www.youtube.com/watch?v=xaELqAo4kkQ
It goes into detail about how the ground lead on the probes is ground and the fact that you have to pay attention to where you are connecting them otherwise you can create a short circuit. Note that all the probe grounds are connected together, so connecting two ground leads to two different circuit nodes effectively shorts those two nodes together.