DeathKnott

well, self explanatory
i want to know how to use the "ruler" (control r) command.
the tutorials say - "use the ruler as a guideline, but neglect to say how to use the ruler as a guideline- which is pretty important

docilebob

Not sure which tutorials you mean, but if you use the move tool (or hold CTRL), click and drag from the ruler, a guide will come out and stay where you drop it, either horizontal or vertical, that you can align via the ruler.
Is that what you mean ?
But that won`t rotate your face for you , only give you a horizontal (or vertical) to guide you.

Doc

Well, I would use the measure tool. With it, draw a line so it passes through the eyes or ears at the same point. Then, go to 'image' > rotate canvas > arbitrary and click OK. This will rotate the canvas (your picture) so that the line created by the measure tool is now horizontal...as well as the eyes, ears and the rest of your image.

Gaussian

Which tutorials? If it's one of this site, then I will change that immediately.