The play will normally be written with character names indicating who speaks which line and in which order. There are plays where this is stated less clearly, leaving more decisions for the director to make, but usually the playwright provides these details.
Stage directions will be given where the writer has a definite idea of what’s required at a particular point. They’re also used to make the situation clear when the action, rather than the characters’ words, is the vehicle for the plot.
This is an extract from the opening scene of My Mother Says I Never Should:
The layout of television and film scripts is very similar to that of a play script. However, there are technical differences due to the different mediums being used, eg directions such as ‘cut to’ the next scene.