I'm trying to post a picture of a swatch that I made of the first 3 rows of the pattern. As you will see after the 3 rows the long double crochets form a V that will continue throughout the afghan. So, what you do on the second row is that you really do go back three DC, put your hook into the base of the DC and make a long loose DC, bring the yarn up to the level of your regular DC and finish the DC.
Then on the 3rd row you will DC into the 3 regular DC on row 2 (not the long DC) and make another long loose DC back into the same stitch that you made the first long DC into - that forms the V that you see in the swatch.
From the instructions it looks like the V's match up all the way throughout so that you will have a diamond pattern of them when you finish the afghan. I printed the pattern and would like to make it sometime, but it will have to wait till after all my Christmas stuff is finished. Be sure to make your beginning chain loose, mine is too tight. I usually use a larger hook to do the chain for that reason.