How do i work this thing?

I just got a used Sega CD from a fellow college student with the warning that it might not actually work. It turns on and seems normal, but how do I open the disk drawer? And what does this "lock" button on the left side do?

You have to open the drawer with your control pad from the menu screen. Turn on the system let it check for a disc then press the start (or the C) button this will bring up the menu screen from here select the "Eject" button, voila! it's open!

The Lock Switch on the side is to hold the mixing cable from the Genesis' headphone jack out of the way of the CD drawer.

If you don't use the mixing cable the lock isn't used.
actually simply hitting the reset button will do the trick for opening the tray.. just like it says at the bottom of the screen too.
Ooh. I thought it might be something like that, but I didn't carry this thought through to actually paying attention to the screen. I will go try that now. Thanks!
Yah Arakon's right, I forgot to mention the reset button open command, It doesn't work with my japanese Mega Cd, so I never use it, that's probably why I forgot to list it.
what i wanna know is what i do with the mixing jack in the back

also when i mess around with the audio CD player i get it into a black screen with details in the corner. Is there actually a point to this feature or is it just if you dont like the VU meters
the mixing jack is meant to be connected to the headphone connector of a genesis 1. that way you get both audio signals mixed and can connect the scd's RCA jacks to a stereo for full sound over it.