I recently purchased an adjustable standing desk base, but initially just dropped a 2'x4' birch plywood board on it. It was a nice introduction to working with a standing desk, but the working space was too small and the edges were very pointy. I wanted to see if I could make a nice desk from these boards from my father-in-law. He reclaimed them from the attic of a house on the Eastern Shore. Pine, I think, but wide (about 16") and very dirty and rough.
So first I cut the boards to length. I choose to cut them at just under 6 feet of length. It turns out that the boards weren't entirely straight. I ripped both of them to 15 3/8, since that was the widest I could do and have the edges parallel. The second (wider) board actually varied from 16 1/2" to 15 3/8" from one end to the other.
After ripping the boards to get a straight edge, my next step was to biscuit join them together. It was my first time using the joiner, so I was pleasantly surprised at how easy it was. I put the boards next to each other, and drew a pencil line straight across every foot or so to make sure the pockets for the biscuits were in the right place. Then I aligned the joiner with the pencil lines on each side to make the holes.
I put glue on each side of the biscuits, put the biscuits in the holes, then clamped the boards to each other, After some initial issues, I also clamped the boards down to the saw horses to keep it from buckling up in the middle. Then I let it dry overnight.