I am a new RN but.....I believe vented tubing is the tubing that has multiple ports along it. When a small air bubble get in the tubing, you manipulate the tubing so that the air nears a close port. You can then flick the port and the air escapes.
Non-vented tubing must be backflowed or advanced/re-primed to rid tubing of air.
Primary tubing is used when infusing 1 or more fluids. It is connected and hung with whichever fluis is used the most/continually such as NS. The tubing itself is long with a few "y" access ports. I believe the kit also comes with a blue hanger of sorts (if not primary, then in secondary).
Secondary tubing is used for "piggybacking" and infusing an intermittent fluid. The tubing is a little shorter, and doesn't have the "Y" ports.
When hanging a "piggyback" w/ secondary tubing, you use the blue hanger with the primary bag. The hanger allows the primary bag to hang lower than the piggyback, which is necessary for the system to work. You connect the piggyback or secondary tubing to the primary tubing. The primary tubing gets fed through the infusion pump. Pump is set for both primary volumes and piggyback volumes. After piggyback has been dispensed, the primary kicks back in. This helps prevent your line from running dry.
I know it's a lot, but I hope I explained it well. If I am wrong on anything, please feel free to correct me as I love to learn!!!