Simple GPIO Output

I am trying to do some simple GPIO output, just to make sure that I can. So far, I have spent around three hours and still, no success. I have tried with both BoneScript and a Python library, and nothing has worked. So, now I have a few questions:

  1. Is there an easy way to figure out which pins are which? If so, how?
  2. How can I know which pins are reserved?
  3. Are we blocked from using pins that are reserved? If I addressed the wrong one, could I break something?
  4. How much power do the GPIO pins supply? Given what I would expect is a low amperage, could it break anything? (as I have probably demonstrated, I am not very experienced with electronics)
  5. Does the output change based on if the board is being powered off of USB or 5V barrel?
    I hoe someone can supply some answers…

US or DC powered has no affect.

GPIOs can supply 4ma to 6mA depending on which ones they are. Defined in the processor datasheet per pin

If you drive into a GPIO that is set as an output, you could damage the device. All GPIO pins are set as inputs on power up. Refer to the datasheet.