Inside the Flash there is a capacitor which is a
cylinder that holds onto power; the charge goes through the capacitor and it
slowly releases the power. Capacitor charges when turned on and when the
shutter is activated the flash is instructed via a sync cord or wireless
control to release the charge of light through its bulb. The power source of a
flash is usually a battery or a floor pack.
The main purpose of using a flash is so a short bright burst of light
spills on your subject when you release the shutter.
The flash sync ensures that the flash goes off when the
sensor will be most receptive because of the state of the shutter. There are
other types of flash sync such as red eye reduction and second curtain.
My Nikon D60 Maximum flash sync is 1/200 second.
