Sound can be recorded directly into the camera or separately.
The sound recordist does the taping and either operates the boom or directs the boom operator to manoeuvre microphones to capture the sound.
The sound recordist also makes sure to capture the ambient sounds of the location, including the neutral aura of the environment (called the room tone, buzz track or presence). This room tone can later be mixed into the final sound at the editing stage to prevent gaps in the soundtrack. Without it, the film may sound awful.
The sound recordist may also record other environmental sounds that ultimately get mixed into the soundtrack, adding to the realism of the final film.