Flashbacks are narratives that point out details of the story or character that already happened in the past. Writers of novels and movie scripts for example frequently use flashbacks to add more details on an ongoing plot. As a particular story unfolds, some details about the real plot may not be fully revealed or understood if some history is not added to the mix. The history part of the story or the flashback sequences and details may be injected at many points of the story to give out some details and clues on how the story is going or how a particular subplot is to unfold.
Many writers also use flashbacks to give depth to a particular character. In many novels and scripts, some writers may present characters with seemingly mysterious personalities. As a particular story is unfolding, some flashback scenes may be necessary so that readers or viewers can fully understand the personality of a particular character. Sometimes it will be difficult for viewers to fully understand how a certain character is projected in the story unless some glimpse of his/her past is presented. In this particular case, some scenes or situations from the past may provide a crucial clue to the actual personality or character and therefore giving it more depth as the plot unfolds.
Using flashbacks may be common for writers but there are also certain rules regarding their use. The most basic of these rules is to ensure that readers are able to connect the flashback to what is going on in the present. Flashbacks also need to be introduced properly so the audience or readers can easily grasp that the following scene or sequence happened in the past rather than in the present. Clues from the past may be presented in a single flashback while there are also times that clues are given in several flashback sequences.