I may be a perpetual noob

but I never had this with HPs I had at my old job, nor with more recent Okidata OL400 laser, nor with the Epson Stylus Photo "toy" which ran out of ink, whereupon I decided to buy another laser.
I don't know where the heck the button on the console is supposed to be - for printing a test page.
I see one thingie sticking out below three light-indicator panels on the left.
Then another thingie sticking out near the base on the left, which I imagine is supposed to disengage something or other for replacing the toner?
Believe me, I had already tried pressing both of them, but nothing happ...
Hey, ONE MINUTE! guess what, I fooled around a bit, and after again pressing the lower thingie, somehow I succeeded in flipping the front facade backward, whereupon I realized there's no toner inside the printer!!! :Q

So I checked inside the packing again, and now noticed the used toner cartridge inside grey plastic packing (which was camouflaged among the rest of the grey packaging) & which I'm now terrified of opening for fear of unleashing I know not what.
The guy never told me in the email that he was packing the toner separately. So, where do I go from here? Is there anyone here with experience at installing used toner cartridges into the HP 6L? Also, does it need to avoid exposure to light?