Not every gym has a T-bar Row. But this is the next best whole back exercise after pull ups. Some gyms will have a station where you can jab a bar-bell end into a corner and and row the other end with weights. This is also good, but it will be much more difficult to keep your lower back straight and tight to prevent injury.
Lean down on the abdominal pad, aiming to put the edge of the pad at your upper chest. Grab the handles and pull up, focusing on tensing your back and not your rear delts. Do not let yourself arch your back rearward just to complete the pull. If you can’t do the rep with your chest on the pad it doesn’t count.
In addition to building immense back strength, this exercise will give your back thickness. The most recognizable growth will be along your spine as you build a nice trench. You should get fairly regular gains on this exercise.
Note: Here is an image of the modified T-Bar Row, described above, where the bar-bell is put into a corner.