e-r-a-n:
thank you for all your explenations,
bob & Peter, you made it pretty clear to me what i need, which is the on/off switch which is the relay.
and an arduino kit that eventually will connect to the relay, that will do the on/off switching.
How can i tell which relay should I buy? The powertail suggested by Peter is capable of 15Amps, how can i tell if its enough?
also, which arduino kit should i buy?
You need to know the voltage across the on/off switch and the current that runs through it to make sure the relay is bulky enough.