Barthes was fairly over-educated for his time. He wanted to establish a way for other people to deepen their understanding of literature, to get them to seek for subtext...etc
It'd appear that Barthes didn't intend on composing the theory, but more like stumbled upon it via practice. His "Semiotics" concept was quite revolutionary for its time: he suggested that the linguistic text for a certain tangible thing may not actually point at the object itself, and that it may have different meanings and differential understandings. For example, understanding that red, isn't just a colour, but also that it may signify danger, blood, patriotism...etc
Barthes based his theory on Saussuer's "Theory of sign", which contemplates that "Sign" is composed of a signifier, the signified and the referent.
Signifier: The actual shape or form. For example, the word "Pigeon" is a jumble of the P, I, G, E, O and N letters.
Signified: The meaning of the shape or the form. For example, knowing that a Pigeon is what it is, a bird, more than just a word.
Referent: The individual message of the signifier. For example, knowing that a Pigeon may stand for peace. (Like an Icon)
(Saussure to the left, Barthes to the right)But how do Semiotics relate with media?
What Barthes and Saussuer are actually suggesting is that verbal communication can be broken down into more meaning. The equivalent of including body language into the interpretation of what someone is telling you. Saying that by mentioning "Red", you're not just talking about a colour, you're talking about blood, and therefore war, or talking about danger, and therefore bad predictions... So on & forth.