The official TRX app is quite expensive (and maybe worth it) but if you want a less expensive way to get into TRX youll like this app. There are a variety if exercises to get you started with TRX. The videos clearly demonstrate each exercise and there are routines you can follow too.
I would have liked a little more explanation for each exercise though. While he shows correct technique, what is incorrect technique and what should you avoid? Its easy to make mistakes when youre first leading TRX. Demonstrating common mistakes with each exercise would be helpful.
Shawnuff about Suspension Strap Gravity Training: Bodyweight Resistance Workout Videos