se is one of the four relationals, one of the four particles that stands in place of what would be a verb in English. Relationals tell one what to expect in the rest of the sentence. Se expects an object (such as a thing being passed from one person to another, or speech, or a feeling) and expects that that object will have a source (someone speaking, for example) and/or a beneficiary (such as someone experiencing a feeling). These may not always be expressed overtly, but they are considered to exist.
se, by itself, uninflected and followed by a simple animate noun phrase or a name is often used to introduce characters. The idea is that the unexpressed source is the person speaking or narrating the story, and the unexpressed beneficiary is the person addressed or the audience of a story.
So, in the first sentence of the North Wind and the Sun, we get introduced to our two characters using this uninflected se.