I'm just curious 'cause I am gonna do it in my game. And I want to know what is the difference between them.
You may not be prepared to create a game if you're unaware of this method.
script.Parent
Gets the script's holder
script.Parent.Parent
Gets the script's holder's holder
So for example we'll place our script in a Part
which is located in Workspace
Here's a visual: script > Part > Workspace
script.Parent will connect to the part.
script.Parent.Parent will connect to Workspace.