Arduino Connection's

I have two Arduino's, i know i can communicate with serial between them. I just want one signal. They have the same power supply. Can i just connect a digital output directly to a digital input or does it need a resistor somewhere . If so what value and were do i put it. Thanks in advance for the help.

I know this is probably very basic but i just don't want to make a stupid mistake and blow anything up.

An input is an high impedance load and should not need a resistor unless you wanted to drop the voltage, although a 470 ohm resistor couldn't hurt in case you accidently set it to output