Yes the bottle is under the seat (you can get a small bag on top and next to as well).
The red handle is the trigger.
The silver U shaped part is the safety catch. From the RHS front seat using thumb press the safety bar in and turn round backwards. The system is now armed. Pull the trigger up to fire.
Remember to take the pin out of the bottle before flight (Pin not shown here) but if you cannot see it and its attractive orange streamer then you should be able to see it behind you hanging from the headsets hook to remind you the system is armed.