Hello guys! I wanted to ask if an arduino uno's output voltage can possibly turn on a 5v or 12v relay? We went to a electronics shop and tested it, the relay didn't clicked. It did click when we supplied it from a electrical outlet source. It is possible we could mutliply the output voltage made by the arduino? Thanks in advance.
No, the Arduino cannot power the relay. Your power source might be able to, just don't push it through the Arduino first. What the Arduino does is provide the signal if the relay is on a module, or through your own setup of transistors/optos/mosfets/whatever.
Google these words:-
arduino connecting a relay
Lots of examples of how to do it right. Note you will need a diode across the relay.
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).