Suspense is the growing interest and excitement felt while awaiting a climax or resolution. This is what keeps an audience "at the of their seats" in a thrilller movie. A great example of the use of suspense is in What Lies Beneath, here is how it is done:
The figure is revealed to be middle aged woman taking a bath; this is the start of the film. The female character tries to turn on her hair dryer but jumps when it suddenly clicks back on; this suggests she is a vulnerable character which leaves viewers wondering what would happen to her.
The non-diegetic music that accompanies the opening add to the tension, the eerie music begins before the opening with builds up through the titles (crescendo). This creates "nail biting" tension as it seems as though something is coming. The music is the main root of suspense as it gives the audience an uneasy feeling before the opening has begun.