Step 1: Download Software
Download the Arduino IDE software for Mac OS X, Linux, or Windows from arduino.cc
Step 2: Connect
Connect the Arduino to your computer using the USB cord & launch the Arduino app.
Step 3: Connect LED
On the computer, in the Arduino application, go to "Tools: Board" menu & select Arduino Uno. Then from the "Tools:Port" menu & select the new serial port with "Arduino" in its name. Open the sketch dropdown menu & go to "File: Examples: 01.Basics:Blink. Click the arrow to "upload" the sketch to your Arduino. Connect a LED bulb in which the longer leg is in Digital Pin 13 & the shorter one in the GND pin on the Arduino board