Stand up straight and place the barbell behind your neck so that it rests comfortably on your shoulders and traps. Hold the bar by placing your palms at a width that is comfortable for you. This is your starting position.
Lower your upper body down as if you are taking a bow all the way until your (upper) body is parallel to the floor. You should be looking straight ahead of you into the horizon. Then, raise yourself back up to the starting position.
Repeat entire movement for the desired or prescribed number of repetitions.
Perform this exercise in a smooth and fluid motion
Keep your back straight at all times
Don't jerk yourself up on the way back as this may result in lower back injury
SPECIAL NOTES & LEVEL of DIFFICULTY VARIATIONS
To increase the level of difficulty, slow down the movement or load the bar with light weightplates.
This is a classic exercise that is great for your back. It's easy to do and has great effect on strengthening your back muscles.
It's good to point out that it's not necessary to load the bar too heavy. In fact, this may be counter-productive as it increases the risk of injury. Thus, a lightly loaded barbell will do for most people.
Furthermore, it's imperative that you warm-up properly before you do this exercise. Getting right into it without sufficient warm-up may hyperextend your back muscles. This is something that you don't want to happen.
Finally, this is an exercise that you can do anywhere - the park, the gym, your home, even office. All you need is a bar or stick that you can put behind your head and across your shoulders. You don't even need to have a loaded bar unless you are at the gym.