Keeping a neutral spine while bending over is an important position for the health of your back. Having suitable mobility and strength in this position will reduce the chance for back injuries, and help with other exercises that require being in a similar position (deadlifts, kettlebell swings, etc.). If you can't get into the setup position with an approximately 30-45 degree leaning angle, you'll need to work on your mobility first. Once you can achieve this position then you can begin to load it with an exercise such as this.
Different angles through the torso can be used to shift the focus on the targeted muscles. You can use any angle from having your torso parallel with the floor to up at 45 degrees. Any higher than this and your row will begin to feel like a shrug movement instead. The only rule with the angle is that you keep a neutral spine when in that position. If you can't stay neutral while bent all the way forward to parallel then that position won't be safe to row in.
As this position is mastered you can also use other equipment - resistance bands, cable machines, dumbells - all can be used for variations on the bent over row.