relays are somethin that scare alot of people but the easy way to think of it is that its a powered switch to turn somethin on or off. ill try to draw or find a picture in a bit. here we go:
and heres mine:
so on the sides are 86 and 85. these two are the "trigger wires". you will use these two to turn the relay on and off. when power and ground is applied to these leads, they will power an electromagnet to switch the contacts inside. polarity doesnt matter on MOST relays, some have a diode, but they will be marked as such on the case, and the polarity does matter on those.
down the middle is the 87, 87a, and 30. as you can see from the first picture 87a and 30 will be connected inside while the relay is at rest (not powered). hence the "a" on the 87a. when you power the relay coil (85 and 86) the 30 will then join to the 87, and when power is removed, the 87a and 30 will be rejoined.
i may add to this later, but ill leave it off here for now