"Start (Night 1)" starts the campaign that slowly amps up in difficulty, or you can start a custom night by going into "Extras" -> "Custom Night" -> (change the sliders that appear, the further to the right they are the faster they'll move) -> "START CUSTOM NIGHT".
If you meant the gameplay, the idea is to keep them out of your office until 6AM, move the mouse to the left and right to pan the camera around the room and move it down to open/close the cctv system, the girls need the doors closed on them if they get too close and will retreat back, Bucky the Stag can only move if you're not watching him with no way to send him backwards and Vulpy the Fox will slowly wake up if the cctv system isn't open.
The Foxy character is a femboy, you can see him sat on the floor in the main menu