Understanding a simple circuit

I'm new to the Arduino, and I don't really understand how it works.

With the standard blink program, where does the power come from? A pin doesn't transmit volt and ground is the end of a circuit and will/should therefore always be at 0 volt, right?

You can certainly drive an LED with a digital output, but the onboard LED on most Arduinos is driven by an op amp.

A pin definitely does "transmit volts" when it's configured as an output, so I'm not sure what you are talking about.

Perhaps you meant ampere, not volt. The data pin outputs 5V. But don't put anything to ahtually work with that, except a led together with a proper resistor. Or something that uses equally little current. Like one micro hobby servo.

Internally each pin has an nFET to ground and a pFET to Vcc (the supply rail). When its an
INPUT they are both off, when its an OUTPUT one of them is on. These FETs have an on-resistance
of about 30 to 40 ohms (when the chip is powered from 5V), and tolerate at absolute most 40mA.

So the power comes from the supply rails. When an output pin is HIGH, the current flows into Vcc
pin on the chip, out the output pin, through the load to ground.

When an output pin is LOW, the current flows from the supply through the load, into the output pin
(confusing!) and out of the ground pins on the chip.

Be careful to separate notion of current going in and out from a signal going in and out - they are
independent concepts.

A pin doesn’t transmit volt

The shortest answer I can give here is “Yes it does”.

I guess it would be wise to ask you what YOU think comes out of a "pin". Not trying to embarrass you, just think it would be wise to correct wrong assumptions now, before they get ingrained in your brain.