Newbie question, help would be great!!

I just started working with arduino so I don't understand everything yet but I'm trying to make a project in which a photoresister senses the presence of someone in front of it, and then a song from a greeting card sound chip is played. I already have the photoresister set up with the example program for blinking LED 13. Altering it seems straight-forward, but I don't know how to use the digital output in order to close the circuit for the music. There are two little metal tabs that just have to connect to make the music start, so if I have wires running from them, where do they go? I'm still trying to understand the schematic I would need to control the sound. I'm aware that this must be a really dumb question, but help would be much appreciated!

Well that kind of depends on the power source on the card.

I would put a volt meter on the 2 tabs and determine which one is ground and also see how much voltage is running threw it. I may be wrong but i'm pretty sure the card uses 3.3V.

I think it's 4.6V. What does that mean, in terms of the route I should take?

Well the 5V from the arduino may be too much but once you ID which of the contacts is ground then you tie that in with the arduino's ground. Then the other contact gos to one of the digital pins. Then all you have to do is digitalWrite(pin, HIGH). But the 5V may burn out the card. So make sure its 5V and make sure you ID which contact is ground.

It may help to post a picture of the sound thing.

You could also just use a simple transistor and a couple of resistors to do the switching.

Using the Arduino pins would be ok if the voltage is less than 5 Volt AND the current is less than 40mA., but i would go for the transistor solution.

Check this :http://www.rason.org/Projects/transwit/transwit.htm or google "transistor as switch", it's not complicated at all.

I tried a transistor, but no luck with that. I just made a digital pin the output so that it powers the speaker when the analog input shows that there's enough light past a threshold. I'm going to tape it to the inside of a cookie jar lid, so when you lift the lid it should play :) Thanks for the help so far. My only problem is that the arduino will sometimes not get power from the computer, except when I touch the power selection jumper with my finger. Then it starts working. I don't know why...