First, clip four (4) white rods into one (1) white piece as shown in the first photo. Then attach pieces to each side of the white connector as shown ...
Step 2: Firing mechanism
I've provided multiple pictures so it can be more easily constructed. Just connect the catch to the trigger with a white connector and hinge it all on a second white connector. Also note that I wrapped the trigger in black tape; this is highly suggested to reinforce the trigger.
Don't forget the rubberband to hold the firing mechanism down until the trigger is pulled.