Suspense is the main feature present in any thriller you will ever watch. It’s a feeling of uncertainty and anxiety about the outcome of certain actions, most often referring to an audience's perceptions in a dramatic work. Suspense is not exclusive to fiction, though. Suspense may operate in any situation where there is a lead up to a big event or dramatic moment, with tension being a primary emotion felt as part of the situation. A well director known for his excellent use of suspense is Alfred Hitchcock, an English filmmaker and producer.
An audience experiences suspense when they expect something bad to happen and have (or believe they have) a superior perspective on events in the drama's hierarchy of knowledge, yet they are powerless to intervene to prevent it from happening. Suspense is what makes a thriller differ from a horror film, as thrillers' main characteristics are a good story line and suspense.
Jaws
A classic example of how affective the use of suspense is, is in the well known Jaws, when false sense of security created by the director worries the audience by building up the idea that there is a shark amongst the innocent people who are portrayed that way through the laughter and short reverse shot between small children and their parents, however in reality its not a shark at all but two children playing a prank, and once the audience are clam again the real thing hits in almost like the classic example of the boy who cried wolf. Here the suspense is created through the dramatic music and pace going from slow to fast as the man runs up to help the real people in danger.