Slingshots are the objects above the flippers that kick the ball in the general direction of each other and towards the outlanes due to their upward angle. The lower playfield layout for modern machines has become a standard of two flippers, two outlanes, two inlanes, and two slingshots in a standard layout. For example, here is a 1977 Gottlieb Mustang EM game illustrating the standard layout that has remained mostly unchanged since:
The mechanism for slightshots involves a coil under the playfield that fires when a ball hits the rubber ring of the slingshot, closes one of two switches to register the hit, then propelling the ball in the opposite direction.
Configuration for slingshots is not limited to just the standard layout, so home builders are free to layout slingshots in whatever manner they like. Occasionally even manufacturers themselves deviate from the standard layout - for example, Williams Space Station has no inlanes: