MGS4... how do I stealth kill...?

First of all, I've only had my PS3 for 2 years. Up until now, I just haven't given a crap about Metal Gear Solid 4. Now that I'm playing it, I'm having trouble and would like some help. Everytime I grab a dude to slit his throat, I just end up throwing him down on the ground. How can I stealth kill people? I have the knife in my hand, but all I end up doing is throwing people down. Help!

Here is a link to bunch of the control options for CQC (ignore anything about leveling up weapons or whatever because that only applies to the online modes).

Short version: press triangle while holding the enemy with R1 (don't mess around with the joystick too much or you might throw the enemy instead).

Jebus! Hit select and look through the menus. The game will show you how to do everything. Just fumble around a bit in the menus.