1. Downloading to the NXT requires the correct hardware setup
To download, you will do the following:
Write a program
Connect the hardware
Turn on the robot
Run the download command

2. Downloading Step 1: Write a Program
Try writing a simple program, just so that you can learn how to download. Make sure you write something that you will be able to easily observe on your robot.
Open the NXT programming software and use a few sound blocks to create an easy test program.

3. Make sure the robot is turned on!
Downloading
Step 2: Connect Hardware
The LEGO kit comes with a special USB cable that is used to connect the NXT to your computer.
Begin by plugging the cable into the proper port on the top of the NXT brick. Then, attach the other end of the cable into a USB port on your computer.
Make sure the robot is turned on!

4. Downloading Step 3: Hit Run Button
Once everything is properly connected, you can begin downloading. Click on the arrow button in the bottom right corner of the NXT programming software to begin the download.

5. Downloading Step 4: Downloading Info
A ‘Downloading’ information window will appear. When your download is complete, you can remove the USB cable from the NXT and run your program.

6. Review
To download a program to your robot, you will need to follow these steps
Write a program in the NXT programming software
Properly connect your hardware, and turn on your robot
Click on the download button in the programming software
Wait for the download window to indicate that the transfer of information is complete