They indicate, for example, whether it is a news-programme we are watching or a comedy. After all, we have learnt these conventions a long time ago and are constantly confronted with them when watching television. And yet the seemingly most obvious conventions, like first showing a person looking at a point off-camera and then showing an object, which we all interpret as this person seeing that object, does not necessarily have to make sense to a viewer who has never experienced television before. On the other hand, the way we put meaning to what we see on TV does not differ too much from how we understand the world we live in anyway. Still we have to be and are aware of television framing reality.
Conventions nowadays are very different from conventions fifty years ago.
When watching a news programme from the '50s, for example, we cannot but realise the strong political and subjective view-point of the coverage. But it represents the time it was made in. Because we live in a different society nowadays and have knowledge of the past as well as the present, we cannot relate the given information to our own experience and therefore have a distant look at it. So, to make a meaning out of what we see, we have to not only identify the sign but also the genre, referring to the context of the programme, identifying its codes. Reading television is indeed a very complex process that we seem to achieve effortlessly.