Hi Arthur,
To give you even a little more help, there are some key things you want to look for when you are doing the lunges on the TRX.
Facing the anchor, and doing the balancing lunge. Your starting position is with your elbows under your shoulders, leaning back slighting making the TRX straps tight. Then as you step back your arms have room to extend without pulling your torso forward. Couple of things you want to watch for when you do lunges on the TRX, is rounding forward of the shoulders. Try to keep your shoulders stacked over your hips. Avoid using your arms too much, really focus on your legs doing the work. Also, be sure to keep your forward knee stacked over your ankle, some people tend to lean back too much and their forward knee ends up behind their ankle.
Facing away from the anchor, and doing the suspended lunge is a more advanced exercise than the balancing lunge. Once you have your TRX in Single handle mode, place one foot in, and find your starting position. By kneeling the suspended knee down, than bringing the planted foot forward until the ankle is directly under the knee. This will ensure that your whole foot is in contact with the ground, establishing a firm base of support as well as your ability to drive up through the heel and activate the glute of the forward leg. Add gait swings, and jumps to make this more progressive.
There are many, many progressions and variations to both of the lunge positions, and I would recommend you view some of the videos in the exercise library to see how awesome these exercises can be.
Hope this helps,
Hayley Hollander Fitness Anywhere Instructor