What they're labelling "RAW" is "+V", coil voltage. By the looks of it, that could be as much as 20V, maybe more but not much more. Choose your relay coil voltage accordingly.
"Load" is the relay contacts, one terminal goes to the voltage that gets interrupted and the other terminal goes to the device getting switched on/off.
Resistor from BASE to GND is not a requirement... more about good design.
Resistor from BASE to ARDUINO is not optional and is used to limit current to safe value for transistor "turn-on" from 5V Arduino PIN. The transistor is essentially a SWITCH that does "work" when the Arduino ASKS for it. It does "work" that would be unsafe for the ARDUINO pin.
Driving a relay directly can make your PIN (or arduino) never work again. The RELAY is an electro mechanical device that uses magnetism from the coil to move a mechanical switch (close/open "contacts")
[quote author=Udo Klein link=topic=102150.msg767099#msg767099 date=1334943607]
The diode will have a voltage drop, this and the internal resistance of the coil / wiring will decrease the current till it "stops". The formula is dI = U/L dt.
Awesome explanation, thanks guys, I appreciate it; I think I get it now, I'll play with it some more and will find out!