sudomod

Hi guys so I'm currently working on a project and I am a noob so I have tried reading up various things but I'm just wondering about a few things before I get started. I have a hori mini ps4 controller that I want to use to wire the Wii u pad controls to but I am a bit unsure about some things. The hori mini pcb is actually very mod friendly and has everything labelled nicely and I have found other people's wii u mods where they have labelled the wires etc. I just have a few questions if anyone could help me out?

I see people talking about common grounds? What does this mean? Is it different to a regular ground?

Is it possible for me to wire all of my ground wires to the same point on the pcb or is there a better way to do this?

Thanks