[//<86TA>\\]

in a nutshell,
the starter relay closes when you turn the key, that relay then sends power to the starter solenoid switch on the purple wire which energizes the solenoid, The solenoid then closes the starters switch, and current can flow into the starter from the main positive cable, The block is obviously the ground here, and then the starter spins.
Since its a computer controlled car with security and what ever else, i'm sure there are more controls/switches/ect in series with the ignition switch.