Difference between GC and Sub

I am trying to understand the difference in being a general contractor or subbing to a general contractor.
What are the difference in licensing requirements, insurance requirements
I realize aquiring the jobs is what the gc does, but I also know that isn’t his/her only function.

General Contractor = GC

This is the guy hired to run the overall job and is usually in charge of hiring sub-contractors if needed.

Sub-contractor = sub

Someone hired by another contractor (usually a GC) to do a job. In effect the person hiring the sub is making themselves a middleman; either because they can not perform the work needed to be done by the hired sub or because the hired sub can get the job done better/cheaper.

One hires a GC and the GC hires subs.

If u use a cheap alien to sub your work to, you can be fined highly. Someone told me as high as $10,000 per alien. I seen a guy using aliens and he told me he subbed the work to a white female (one of the guy’s girlfriends)(the only one that could speak english), she was the one responsible for the aliens.

Please also note there are GC’s who pull in plumbing, concrete, electrical, etc. & there are ROOFING GC’s who merely sell the roofing job under an umbrella of the entire project & then pull in other co’s under them or have sub crews (a sub crew vs. payrolled employees & everything that goes along with having them on “staff”).