How to supply power from vehicle to a low power device?
I am mostly self taught on this stuff so someone please correct me if I am wrong.

I think you have a slight misunderstanding as to how current flow works. Unless there is something seriously wrong with your circuit, that rating means that it will use at most 1W of power from whatever supply system it is hooked up to (so don't hook it up to a 0.5W supply). I guess the best way to think of it is that the device is responsible for how much current it draws; the PSU will not "force" extra current down into it. 

Current limiting circuits and fuses are used to protect against short circuits because when you short out the power supply (connect the two terminals together), the load resistance drops to essentially 0 and current flow theoretically approaches infinity. You can see how infinity amps of current could break something!

Think about it: 

V = I * R

if V = 30V and R = 0 ohms,

V/R = I (rearranged equation)

30/0 = I (a divide by zero situation)