Free Microsoldering Forum – Ask an Expert
I think that you will need to do some googling in basic electronics. There are so many resources out there, like this one: https://www.allaboutcircuits.com/technical-articles/an-introduction-to-ground/
I'm not sure if this forum is the best place to go over all of this stuff.
The basis of ground in electronics is that every circuit needs a start path and an end path. The end path is always ground. Anyways, it's probably best if you google it to get a more clear definition.
I highly suggest you watch Louis Rossman's introduction to electronics videos. Very logical and easy to understand. Then as Mike says it is all about googling.