Did you read thru all the instructions? Got your tools and supplies all together in one place? Got a helper? OK, then let's start.
First, cut four 11" pieces off the 2x4. I did a terrible job on the cuts, so it was a good move to have the lumberyard do most of my cutting for me. I recommend you do the same. They have a really nice setup.
Then attach an 11" 2x4 piece to each desk leg. Mark off enough space on the end for a 2x4, you'll need it later on for the back panel.
Make sure you attach the 2x4 to the 24" edge. Attach the 2X4 to the "bad" side, it will be inside the desk. Save the nicer side of the plywood for the outside of the desk, do this on both legs.
Make sure you construct both a right leg and a left leg.