Intake vs. Exhaust

[seanpull]

So, I just built my first PC a couple of days ago, but my case only has one fan, so I decided to pick up three 120mm fans. My case is a CM 430 Elite, so if you know it, great, but if you don't, I'll explain it real quickly. It's got a pre-installed 120mm front fan, then it has room for two top 120mm fans, a back 120mm fan, and a side 120mm fan (by the graphics card). Now I hear people talking about intake vs. exhaust, so basically, I'm wondering how do I setup an intake fan? how do I setup an exhaust fan? Also, where should I put my fans? I was thinking one top, one back, one side? but maybe two top, one side, no back? which would provide the best cooling? Thanks for your answers to these questions, I appreciate it.

 

[manofchalk]

Standard layout is that the front and side fans are intake, and the back and top are exhaust. That sets up a basic front to back airflow.
Whether its better to have positive pressure system (where more air is blown in than out) and a negative pressure system (more blown out than in) is highly debatable. But for the uninitiated, a positive pressure system is the best solution.
To make a fan an intake or exhaust is just a matter of which way around it is when you screw it to the case. Usually the air flows out of the "ugly" end of the fan, but you can just plug it in and feel which way it blows. There may also be some arrows on the frame to indicate airflow.