Adafruit Motor Shield

Hi guys,

I am fairly new to Electronics but I am making some progress. :)

I got this shield: Adafruit Motor Shield v 1.2

and I want to use it to power 2 DC-Motors and maybe 1 servo. I did some research but I am still a little confused about powering the shield and the Arduino.

I got the concept that you can power them separately or together but I want to understand it in depth.

If I use the [EXT PWR] on the shield and leave the Power Jumper on the shield my Arduino(Arduino Mega) will be powered by the [EXT PWR] too - right? So the real question is - if i do it like that with an external power source >9V does the Arduino crop it down on what he can take or does it get dangerous for him?

If that is the case I understood the right way to use an external power source >9V is to connect it to [EXT PWR] again but disconnection the Power Jumper on the shield so the Arduino will not get powered by [EXT PWR] - is that correct?

Of course I would then need to connect a power supply to the Arduinos DC Jack to power him and the 5V pins on top of the motor shield - am I right?

I know this does not sound very technical - sorry for that.

I would really appreciate if someone could answer this questions. Even better explain it in detail on how the two are connected and why they can share power or are isolated.