This video is about Grbl 1.1 Limit & home switch Guide

https://github.com/gnea/grbl/wiki/Wir...

Grbl Arduino CNC Wiring Limit Switches
he limit switches are used to detect the physical limits of the working area and to position the head in initial position during the homing process. Properly connected limit switches can increase significantly the reliability of the GRBL the microcontroller pins connected to the switches are very vulnerable to any noise.