my radiators wont heat up or the hot water. the boiler is on and lit.how do i drain the system?

i would think the pump has failed,most pumps have a central cover remove this and give the pump a spin if it stays stopped replace pump,

Not sure why you are draining the system for this problem but any how, turn off all controls and power to the boiler. Find a drain off cock, usually under a radiator or on the heating circuit low level somewhere, attach a hose, open the drain off and drain. You may have a sealed system or a vented system. If its sealed then you can drain and it will not re-fill, if it is vented then the feed from the expansion tank needs to be turned off or shut the water mains going to the tank and drain the whole thing. Vent all the radiators and any manual vents and then your done ready to work on the system, please have some towels or a water proof sheet down by the drain off as these tend to leak from the middle.