I recently bought an arduino and this is the first project that I have (successfully) completed. This is a super easy project and it's mostly to get beginners to understand how arduinos work. I found this project in a book called "30 Arduino Projects for the Evil Genuis". It's a great book and it's very easy to understand! I hope every body enjoys this instructable! The book is slightly outdated so but I can still understand how to do everything. This instructable does the same thing that the book does but explains it in a way that is up to date. Enjoy!

Step 1: Hardware and Software

Hardware:
1 Arduino Uno
1 LED
1 Resistor
1 USB Chord

Software:
Arduino Software

Step 2: The Sketch

For all of you that aren't familiar with a lot of technology terms, like myself, a program for an arduino is called a sketch. I assume that most people that are making this have already downloaded the arduino software but in case you haven't here is a link to the site where you can download it:
http://arduino.cc/en/Main/Software

Once you have downloaded the software, open it up and start a new sketch. Next, click file, examples, digital, and blink without delay.
We are going to tweak this sketch a little. Go to the place where the sketch says "const int ledPin=13;" and change it to say "const int ledPin=12". That's it!

Step 3: Set Up the Arduino

You will see that your LED has two metal rods sticking out of it. These are called leads. Take your resistor and wrap it around the shorter lead of the LED. Next, take the one end of the resistor that is not wrapped around the LED and stick it in the arduino board next to the place that says GND. Now, take the end of the LED that is not connected to the resistor and stick into the arduino board next to the place that says 12.

Step 4: Make It Light Up!

Plug your USB chord into your computer and into your arduino. To upload the sketch, press the arrow that points to the right and your LED should start blinking! To change the frequency at which the LED blinks, change the number in the part of the sketch that says "long interval=1000" and then upload the sketch again. Enjoy!