Just a quick question. Do you need to attach/clip in the l239d motor shield unto the arduino uno or can you simply have it next to the arduino and control your dc motors from there? If so, how?
If you provide a link to the shield you're using we can look at it.
You can usually use a shield off to the side of the Arduino but you need to connect the appropriate pins together using wires.
Usually you use a shield on top of the Arduino. This all the needed pins get connected automatically.