The series of photos above illustrate how to dock to a host pack. You wear your kit bag underneath the main pack. When you put on your main pack, just dock the kit bag to it. Before taking off your main pack, undock your kit bag. There are slightly different ways of doing it. Evan wears his sternum strap over the kit bag, Scot wears it under. Neither of us ever adjust the top straps on the Kit Bag (unless wearing over a PFD), but the side straps get frequent adjustments based on docked / undocked and various clothing layers.
The extra slick clips are spares in case of breakage. Stow them inside your Kit Bag and forget them until you need them. It is rare, but you can accidentally break them in the process of opening and closing them. Once fully closed, we've never seen one break. With the use of slick clips, you can attach the docking straps to just about any shoulder strap out there. If that doesn't work with your particular pack, you can also get creative with parachute cord loops among other things. The grimlocks on the Kit Bag itself gives you lots of different options.