Sorry for that smart ass "Engineering" answer by the fellow poster! Check out this link:

http://wiki.owwm.com/(S(30jmnh45vffqwhrx4vtqutmm))/Default.aspx?Page=Motor%20Starter%20Wiring%20Diagrams&AspxAutoDetectCookieSupport=1

Basically the steps involved in starting a motor via magnetic starter are simple (3 phase example):

1) Press and hold the NO (normally open) START button which closes a low-current switch supplied from an auxiliary circuit

2) Relay coil(s) are energized closing 4 contacts - 1 large contact for each phase and one auxiliary that is wired in parallel with the NO start button. The auxiliary contact acts like someone holding the start button. The START button can now be released and the coils remain energized.

STOPPING:
1) Press the NC (normally closed) STOP button which opens a switch supplied by the auxiliary circuit.
2) Power to the auxiliary circuit is cut disengaging the coils of the relays opening all 4 contacts.

The Auxiliary Circuit is supplied by the difference between any two of the three phases. If the STOP button is pushed, power to the auxiliary circuit is cut. The thermal overload portion of the starter is a separate part which is not affected by the control circuitry. It simply disconnects the 3 main phases if a load in excess of the rated load is seen. It also disconnects the power to the auxiliary circuit. This stops the motor completely until the thermal overload is reset and the motor is started again by operator intervention.