Video is underrated but you did a good job explaining it. If I may ask, I am completely new to Linux -- what are groups for? With Windows, I know security & permission groups. With Linux, you have chmod to set the permissions but what's the point of that if all groups have equal permissions? I must be overseeing something because it doesn't make sense at all.
Each file has file mode bits attached to it, that is what chmod changes. A file has an user (owner) {u} associated with it, a group {g} and user not in that group {o}. When invoking chmod, you assign privileges (read, write, execute) for these 3 categories. So when put users in a group and then associate this group with a file with a group, you can set a privileges when interacting with the file.
