Consider a block on a ``frictionless'' inclined plane.
We'll talk about
friction in a little while so don't get too bothered by this term.
Basically it means a very very very well greased surface, so that
there is no force acting along any direction on the surface of the
plane. We have this block of mass m that is attached
by some string to a force meter. We want to know how much force
is registered by the meter. If the angle 
that the inclined plane
makes with the horizontal is zero then this force will be zero.
But for other angles what is the answer?
Let's follow the handy-dandy rules of above to quite effortlessly solve this problem. Once you've gone through this once. You should try to solve it again without looking.