Superposition theorem is one of those strokes of genius that takes a complex subject and simplifies it in a way that makes perfect sense. It is very useful for solving tricky electrical circuits, Just go through the following article to get complete description and illustrative examples on Superposition Theorem.
formatting link
The strategy used in the Superposition Theorem is to eliminate all but one source of power within a network at a time, using series/parallel analysis to determine voltage drops (and/or currents) within the modified network for each power source separately. Hope the above article helps you in your exams .. :-)