The T-bar row focuses mainly on your back including your rhomboids and lats.
First of all, this is a plate loaded machine so add an appropriate weight for you at the top of the T-bar.
Stand up onto the T-bar with your stomach against the rest pad. Grab the bars with both hands and move the T-bar into the middle position. Pull upwards towards you making sure your stay on the rest pad, squeezing your back. Lower in a controlled continious motion.
This instructional video is shown by Daniel Ciastoch, a PT at the Ascendancy.