Understanding audio port schematic
The other 2 pins are usually normally-closed connections for the pins adjacent to them; plugging in a jack moves the adjacent pins away from them, breaking their connection. They are used either as sense or to shunt audio to internal speakers when no headphones are plugged in. OTOH, the fact that they aren't given in the schematic may mean that they are only for structural support.

A circle at the end of a wire indicates an external connection point where another wire may be connected either for some utility purpose or to make it part of a larger circuit.