Here are the definitions of the three terms, taken word-for-word from Looking at Movies: An Introduction to Film (W.W. Norton & Co, 2006; http://www.wwnorton.com/college/film/movies2/glossary.aspx).

real time: The actual time during which something takes place. In real time, screen duration and plot duration are exactly the same. Many directors use real time within films to create uninterrupted "reality" on the screen, but they rarely use it for entire films. Compare cinematic time, stretch relationship, and summary relationship.

stretch relationship: A time relationship in which screen duration is longer than plot duration. Compare real time and summary relationship.

summary relationship: A time relationship in which screen duration is shorter than plot duration. Compare real time and stretch relationship.

Alongside those definitions, this source identifies a fourth relationship that is worth mentioning:

cinematic time: The imaginary time in which a movie's images appear or its narrative occurs; time that has been manipulated through editing. Compare real time.

Judging from these definitions alone, I think it’s safe to say that “real time” is the most common relationship of screen duration to story duration. In all (or maybe nearly all?) movies that we watch, much of the action on the screen passes in “real time.” We hear the characters talking as they talk, watch them as they move, and so on. In just about every film, of course, there’s usually some “summary relationship,” too. We don’t track their every move and hear their every utterance, just the significant ones. The film might skip hours, days, years, even centuries in just a flash, as needed to keep the story moving and to allow the film to fit within the time constraints of one to three hours. “Stretch relationship” is the least common of the three relationships.

The specific editing techniques vary a lot and are worth considering, as do the effects of stretch and summary relationships. Things usually slow down in the film for psychological or dramatic effect, such as in Katniss’ tracker-jacker-poison-induced hallucinations in the film adaptation of The Hunger Games (the distortions on the screen very effectively match Katniss’ distorted perceptions) or the nearly-frozen-time martial arts sequences in The Matrix (everyone seeing those fights for the first time probably gasped; I know I did!). Sometimes the story jumps forward in time for the same reasons. A fade (usually to black or white) can indicate simply that time has passed or that the character through whose eyes we are seeing is regaining consciousness after some time has elapsed, for example.