I want to connect a female 1/4 jack to my arduino and use a male to male 1/4 inch cable to connect straight into the input of my guitar amplifier. I am unsure how the circuit should be wired for this to make sure I am sending the right voltage to the amplifier. And I was also wondering if sending a tone to the amplifier would be the same as sending a tone to a peizo speaker.
If u explain better what you want to do, schematic if you have and code, would hep, as we dont have clairvoyants here !!
And I was also wondering if sending a tone to the amplifier would be the same as sending a tone to a peizo speaker.
Yes.
Just connect the arduino output to the amplifier input through a series 0.1uF capacitor.
I agree with Mike, a capacitor should do it. Just turn-down the guitar amp before you start, because the signal will be on the "hot" side. If the signal is too-hot, so that you always have the volume set to '1', let us know. There are easy ways to knock-down the signal with a couple of resistors or a potentimeter (volume control) on the Arduino's output.
And I was also wondering if sending a tone to the amplifier would be the same as sending a tone to a peizo speaker.
Yes... But LOUDER, and of course the guitar speaker can reproduce low-frequency tones that the piezo cannot. What would your guitar sound like played throught the piezo? 
The pitch will be the same (at frequencies the piezo can produce) but the tone/character will be different.
BTW - Be very careful with high-frequency tones... Say above 10kHz... You can end-up generating lots of power that the speaker can't reproduce well, and perhaps above your hearing range. So the amp could be generting lots of power without you being aware of it. Guitar amps are usually rugged and it will probably survive, but it's something to avoid.
For the similar reasons, be careful running "test tones" into a high-power hi-fi system. You can burn-out almost any tweeter with a constant 100W 20kHz test tone. And, because our hearing is weak at 20kHz (if we can hear that high at all), you might not be aware of what's going on 'till it's too late.
Thanks guys.. also will I need to run any voltage/ground to the female 1/4 inch connector from the arduino or is the only input that the amp will need is the output of the frequency I want to play from the digital pin?
Yes yo need the ground on the body of the jack, with the audio on the tip.
Thanks again for the information, but like you said it is blaring loud with the amplifiers volume level at 1. You also hinted at an easy fix to this I was wondering what ohm resistor you recommend and if it matters if you put it in before or after the capacitor. Also the capacitor I got wasn't a .1uF it was a .068uF, but I don't think that really effects anything.
Use a potential divider to cut down the signal. Output -> 10K resistor -> capacitor & 1K resistor -> arduino & audio ground.
Experiment changing the value of the 1K to get the volume you need, the smaller it is the less the volume is.