Scene Headings, also known as Sluglines denote any change in location or time in your screenplay.
EXT. WAREHOUSE DISTRICT - DAY
"EXT" stands for "Exterior." You create a Scene Heading in Slugline by beginning any line with one of the common Scene Heading prefixes:
INT. EXT. EST. INT./EXT INT/EXT I/E
"EST." stands for "Establishing." "INT/EXT" is often used for scenes in vehicles.
To create a Scene Heading that doesn't begin with one of these common prefixes, just begin the line with a single period:
.BACK IN THE WAREHOUSE