"Roll it" is a film term meaning "start the cameras".

Several movie production terms are used. All are familiar to native English speakers. A "take" means one continuous piece of action, filmed without stopping the camera; the actors have to make no mistakes during the "take." The Alfred Hitchcock film "Rope" is famous because it looks as if the entire film from start to finish was filmed in a single "take." "Roll it" means to start the camera, so that the reels of film begin rolling. The director waits a few seconds for the camera to stabilize; the actors just stand around. When the everything is ready the director calls "Action!" and the actors begin to move and talk. "Cut" means stop the camera. It often means to stop before the scene is complete because there has been a mistake, or the director wants something done in a different way. While I am at it... the phrase "Lights! Camera! Action!" is a well-known and is (or once was) the series of commands given by a director at the start of a scene. And the word "slapstick" literally refers to the device once used at the start of a scene: a little blackboard with the scene and take number written on it, and a hinged wooden board that made a slapping sound to help the editor match up the sound and the picture. For a long time, this device was a symbol of the movies.