1-Awareness of tension - by concentrating on an area of your body, you learn to recognize tension.
2-Tensing the muscles.
3-Letting go of the tensing.
4-Awareness of relaxation - you concentrate on the particular area of your body, and you learn to recognize the feeling of relaxation.
How/When-The best position for practicing progressive relaxation technique is lying down. Some people use this technique just before falling asleep, but you can use it at anytime of the day.
Hope this helps. :)