One of the foundations of furniture making is starting with lumber that is four square, meaning that all four sides are square (90 degrees) to each other. Preparing rough cut lumber is critical when building any project because it will effect how joints come together, how doors will hang, etc. There are eight steps to getting lumber to four square: Step 1: Cross cut material to rough length Step 2: Rip material to rough width Step 3: Flatten one face flat Step 4: Square on edge to the newly flatten face Step 5: Plane the second face parallel to the first Step 6: Rip to finished width Step 7: Square one end Step 8: Cut the other end to the finished length The video goes into detail on way to complete each of these steps so you can work with lumber that's straight and true. Craig Less