12v external power source, Uno

Sorry for such a noobie question, but I've only had my Aurduino for a month or so and don't want to fry it already! I'm working on a tutorial to program an RGB LED strip. The strip is 5m long and I want to use the Uno to write a program and use all 5m. I have the board setup identical to the tutorial with the transistors. In one of the captions it says I can use an external 12v source. I have a 12v 2a wall plug that I'd like to power this with. It says to connect the +12v of the wall plug to the Vin on the LED strip and ground to the arduino/mofset.

Does that mean any of the ground pins on the board? It's the /mofset that got me, I don't know if that means a specific ground pin or not.

Here's the tutorial I'm working on:
http://www.ladyada.net/products/rgbledstrip/

split 12V+ to Vin and the mosfet. Split ground between arduino GND, and LED ground. Control mosfet with Arduino pin.

IIRC (and I'm very liable to be wrong), arduino pin goes to gate, 12V to Source, Arduino pin to Gate, LED positive to Drain, for an N channel.