Learning the inverted row is the first step to performing a chin up/pull up. It teaches you how to properly engage the lats, pack the shoulders and allows you to adjust on the fly. 

The EASIEST way to teach this movement is from the finishing position first, then moving out.

1. Pull the handles back with your elbows slightly past your body with your shoulder blades pack and your lats engaged. Making sure that your shoulders don't roll forward.
2. From there walk yourself forward until you find a position that you're able to hold onto but is only a slight challenge to maintain. That's where you should stand to begin.
3. Keeping the core tight, ribs down, extending the arms and then pull yourself back up.

As you progress, you can slowly work your way towards having the starting point underneath the anchor point of the TRX or suspension trainer. Eventually the final bodyweight progression is to elevate the feet, at that point you should be able to start performing chin ups!