Here's a section of an image from a magazine advertisement. Look at it. If you've never seen the image before, you're likely to wonder, 'What's going on? Why is the young man (you assume he's young because of the signifiers of build, haircut, and dress) covering his face? Is he upset? What about?'
Your mind, in other words, tries to understand this image as a moment in a sequence of events: as a story - a narrative (even though in reality this is just a model paid to pose before a camera for an advertising shoot).
As humans, we have an unshakeable predisposition to force meaning onto things. Think about a picture of a group of smiling people - a man and a woman and two children. We will 'force' onto it the meaning - naturally enough - that this is a typically happy family. But - how can we know this is true? Like the image above, this image works because it cues an existing narrative - in this case a cultural myth of the happy family and all that this involves at an ideological level.