(Complete newbie, forgive my ignorance!)
So I'm trying to run a really simple sketch where one LED flashes, then the other. The problem is I can't figure out how you're supposed to add multiple LEDs to the (Deumilanove) board - from what I've figured out by playing around with it, each LED needs to have one leg into a numbered bit, and the other into GND. There's only one GND bit, though, so how am I supposed to add more than one LED?
Cheers,
Joe
You might need to buy a prototype shield - http://shieldlist.org -
or an breadboard - http://www.sparkfun.com/search/results?term='breadboard&what=products -
you should buy a bundle of wires with that too for easy connection
Those breadboards are interconnected holes so if you connect one to GND you have multiple GND's for all your LEDS.
hopes this helps.
Check the shiftout tutorial - http://www.arduino.cc/en/Tutorial/ShiftOut - about how to use a breadboard
Sorry, I should have said that I have a shield - so all the holes are GNDs, then?
Cheers,
Joe
no not all holes are GND,
most breadboards have 2 long strips for 5V and GND and a lot of shorter ones (group of 5) that are interconnected.
If you look at the shiftout tutorial there is a picture of a breadboard and the 2 dark colums on either side are a GND and 5V array of holes. Notice all black wires are in the same row and all the red are in the same row.
The middle part are rows of 5 interconnected holes.
You should just order one (a few) and start experimenting, they are very easy to use. 
All the holes are not grounds, but you could make as many of them grounds as you need by connecting the Arduino ground to them. Then you just connect whatever needs to be grounded (multiple LEDs) to those holes. Likely, there is a group of holes on the shield that become grounds once the shield is connected to the Arduino. Not knowing exactly what shield you have, we can't give you exact instructions. The next easy way is with a common breadboard. It can be thought of as a hole multiplier. There are usually 2 columns of holes that run vertically on the board, often one is marked with a red line(for power), the other a blue, green, or black line(for ground). Each hole within one of those columns is connected vertically to every other single hole in that column. If you connect a wire from your Arduino ground hole to any of the holes on the black line, then all of the other holes on the black line become grounds as well. A similar thing happens if you connect the +5v Arduino hole to the red line of holes. They all become a potential source of 5v power.
Since I have begun describing breadboards, I might as well finish. The remaining holes on the breadboard are arranged in several horizontal rows. Each row contains 5 or 6 interconnected holes, a gap in the middle, then another 5 or 6 interconnected holes. The holes on the left are insulated from the holes on the right. Each row is also insulated from any other row. These can be used any way you like. Typically a chip (DIP dual inline package) is inserted straddling the center of the board. The end result being that each pin of the chip is now connected to a row of holes allowing easy connection to anything else.
Dustin Maki