The Black Dahlia
The slug line is telling you where the characters in the scene are, whether they are inside or outside, time of day or night. It also tells you where it is I.E residential block, a courtyard, stadium or shops.
The description tells you what is going on in the scene. It talks about their movement/actions so you know every that is happening e.g. “He slows to a jog, trying to gather his thoughts. And then a voice:” this then leads to dialog from an unknown character. This is how the writer wants the scene to work, it is how he wants the actor to play the character but this is just an early draft.
The dialog is what the character (voice over) is saying during the scene and it also tells you who is saying the dialog just above the text. The dialog is always centralised so you know that it is dialog e.g.
This way you can easily tell that at this time there is meant to be someone talking
In this part of the scripts it doesn’t tell you about any transitions that are happening if there are any