arduino - positive vs negative, power vs ground, flow direction

I'm getting very confused about the inconsistency where some people say ground is always negative, and some say ground is always positive.

And some would say, electrons travel from the power source to the ground, but while some would say electrons travel from negative to positive. These two notions would be aligned and make sense if ground is positive, but not according to my Arduino instruction manual, since it's clearly drawn in pictures that the GND port of the circuit board links to the (-) column of the breadboard.

Moreover, according to physics, electrons flow from (-) to (+), so that sounds like anything coming from the (-) is acting as a power source? so which port in my Arduino does the power come from? the 5V port or the GND port? From my first impression, it's the 5V port that's supplying the power, since it's "5V." But is it one of those things where direction doesn't matter?

Just to make it easier for answering:

1) is it true that ground can be positive and can be negative, just a matter of preference and there's no "always?" And if yes, is negative ground the more popular preference?

2) Does the energy come from ports like 5V? Or is it that labeled 5V doesn't mean that's where the power comes from?

3) Do electrons in my Arduino flow from (-)(connected to GND) to (+)(connected to 5V), or the opposite?

Feel free to elaborate if you think it would make it clearer.

EDIT:

By 'power' I really meant energy.