PA0 is Pin A0, this is for activity, which I assume you want.
You seem to be looking at both the power and activity sections of the link I sent, pick the one you want that LED to be and follow those instructions.
Lastly, we'd usually just pick 330ohm resistors - something in the middle. You'll need some resistor or you'll burn out the LED. Unfortunately it depends on what the LED is rated for so I cant just tell you the resistor to get. But 330ohm is generally safe, though may be a bit dim. You can usually pick up packs of resistors of varying values for cheap - handy for projects like this.