So the "rule" (ok suggestion, I like that) of thirds is a set of imaginary dividing lines that break the frame into three sections vertically and three sections horizontally. Think, tic-tac-toe board. You then take those lines as suggestions on where to place the focal point (what you want your viewer to look at). What this does is prevents the subject from being to centralized while same time leaves breathing space from the edge of the frame. It also gives the image a sense of purpose, like you took the time to place the car where it is in the frame, instead of slightly off the middle etc etc...
Like so...
Is this starting to make more sense?