Run the tubing by beginning at one end of the conduction path for the air or liquid you want to use. It is better to begin at the source, such as the main water line or air compressor, and then stretch the tubing to where you want to go with it.
Use the razor knife and make a straight, sharp cut to the end of the plastic tube. Even the factory edge of a new roll should have a little cut from the end to make a good seal. The cleaner the end cut, the tighter the tube can mate into the female compression fitting.
Slide the brass compression nut over the tubing approximately 2 to 3 inches from the cut end.
Grab the brass ferrule between your index finger and thumb and work the ferrule over the plastic tube. The fit will be a little tight, but this is what you want. Work the ferrule approximately 3/4 inch from the cut end.
Push the end of the plastic tube into the female compression fitting. Make sure the end of the tube slides "home" into the orifice.
Push the compression nut onto the male threads of the female fitting. The brass ferrule will slide under the nut and into the contoured fitting of the female compression end. This creates the seal against any leakage.
Tighten the compression nut with your fingers onto the female fitting. Finish tightening the nut by using the crescent wrench. As you tighten the nut, the brass ferrule will crimp around the plastic tube and seal.
Perform the above steps for every plastic tube connection you have. Open the valves and test the plastic circuit for leaks.