Type your slugline, which tells the reader where the scene is taking place and at what time. For example, a scene inside a warehouse would look like this: INT. WAREHOUSE - NIGHT.
Type the action below the slugline to inform the reader what is happening in the scene. In a scene that involves a phone call you could type, "John Smith, 30, crouches behind a large crate, clutching a gun. His cell phone buzzes and he pulls it out, checks the screen and answers."
Type the dialogue in the scene as John answers the phone, then type the slug line, action and dialogue of the second location in the scene. For example:
JOHN
You're not supposed to call me.
INT. LIVING ROOM - NIGHT
Jane Smith paces, phone cupped under her chin as she gazes around in panic.
JANE
I'm sorry, I can't take it anymore.
Type the words "INTERCUT John and Jane" in capital letters below Jane's dialogue. Then type John's reply to Jane and go back and forth between them without having to write a new slugline each time you switch the scene. When the phone conversation is done, you can write, "STAY with John as he fumes over the call," or "STAY with Jane as she fumes over the call," to indicate to the reader that we are now back to only one location.
Intercut a scene that doesn't involve a phone call by following the same basic principle. Begin the scene with a slugline, action beats and dialogue (if applicable). Write the slugline, action beats and dialogue for the second location. Type "INTERCUT" and describe what is happening in each scene without typing separate sluglines for the different locations. If you are intercutting three locations, create sluglines, action beats and dialogue for each location, then write "INTERCUT" after the slugline, dialogue and action of the third location.