Drill the holes in the shelves all at once so they are aligned. (something I should have done). I always did like Salvador Dali
Measure about 1/2 inc to an inch on each pipe and mark. This is where you want to drill you first holes.
Drill the four holes in the pvc for the bolts.
Put in a set of bolts, washers, and nuts for the first shelf..
Install the first shelf.
Now measure up 10 inches and repeat the process till all shelves are done.
If shelves are loose, you may want to add some king of back brace to the system.