Open iTunes on your computer.
Connect the MP3 player to your computer via a USB cable (usually there's one that comes with your device when you purchase it.) If you don't a USB cable, you might be able to find a universal one at Radio Shack or Best Buy.
Open the MP3 device on your computer by clicking the USB icon in the bottom right of the screen. (Both Mac and Windows usually open the device automatically.)
Find where you store music on the computer and open that file. For instance, in Windows, you might find an iTunes file under the My Music file in My Computer.
Get songs on your MP3 device by clicking and dragging them from your music storage file to the MP3 software that opened when you plugged in the USB. Safely remove the USB when finished. The songs should now be on your MP3 player.