Very Stupid Question - Intake?

OK I have a very stupid question, so bare with me. I've seen lots of posts concerning "the intake", plastic intakes, Bullit intakes (which seem to be better for some reason, because they are metal vs plastic??). Can someone explain to me exactly what the intake is and does, where is it in the motor, and what the difference is between the different ones available. Also, I have an '00 GT, which has had a Vortech Supercharger upgrade done to it. Is it worthwhile for me to upgrade my intake for performance (and what kind of increase?) or durability reasons? Thanks for your patience with these questions!