Electrical Question (Relays)

[cali_surfer]

I had a question about relays and was wondering if anyone knowledgeable in auto electronics could help me out. On a relay, what do each of the different lugs do? There is 30, 85, 86, 87, and 87a. I know that a relay is like an electronic switch used to take the load off of a switch, when switching a high draw component like an elec. fan, fuel pump, etc..... but I would like to know how these different wires work. This question pertains to the fact that I just bought a keyless entry system and I'm thinking about wiring up power windows to work with my remote...... and the fact that I'd just like to know how a relay works. Thanks for any help.