Shit I haven't done them in a while, I did machine lunges at my gym and that ripped me up pretty good. The machine simulates dumbell lunges and has a sliding pad to push your foot back on.
RaMp4ge- Lunges: Start from a standing position with feet approximately shoulder width apart. Step forward with one foot and squat down while leaving the other foot in place. Your front leg should be bent at about 90 and your back knee should be either slightly touching the floor or just above it. Next stand straight up then step you front foot back so you feet are together again. Repeat as many times as desired. You can either do one leg then the other or alternate back and forth. Barbell lunges are where you have a bb in the squat position (across shoulders holding onto bar with both hands), Dumbell lunges are where you hold a dumbell in each hand hanging down around your sides. Dumbells are probably easier to keep you balance on. There are many variation on lunges and lunge workouts but we can save that for another post.
Cheers,
Scotsman