Electrical question about a light switch?

I'm attempting to repair a light switch for my dad, and I was just curious to know what the amps and volts readings should be for a standard light switch? Also the tester I'm using has various setting on it (it was given to me I'm not all too sure exactly how to use it other than to know wires are hot when the needle goes up), I know its V AC or A AC, amps and volts, but what setting should I be on. 200mV, 2V, 20V, 200V, 600V? Isn't it 20V for a light switch? Thanks for your help