Use a relay board or e.g. something like Control a Relay with Arduino – Tutorial #5 (just the first one I found).
A 328 based Arduino can only sink/source 40 mA on a single pin (there are other limits to consider as well).
So if the relay draws less then this 40mA it should work; you however need a flyback diode over the relay to protect the Arduino (see the schematic in the above link).