where to plug in external speakers

Hello All

Please forgive me for asking this probably simple question, but I'm not sure of the answer.

I just got a Optiplex 380 win7 32bit. I did not order speakers since I have NEC speakers (which I've had for quite a few years) that still work fine. At least they worked on my Dell Dimension 5150 XP machine that just recently died.

The NEC speakers have a power supply and there is a 'black' male plug that should go into the back of the computer. My question is exactly where do I plug them in? There is a 'light green' line-out connector and a 'pink-blue' line-in/microphone connector on the back of the computer. I'm assuming that I plug the speakers into the line-out connector....am I correct? Will I hurt the computer if I plug the speakers into the wrong place? Are there drivers for speakers that I might have to find and install?

Again, please forgive the maybe stupid questions but when it comes to computers I'm not very knowledgeable about the inner workings.

Thanks in advance

Barb