http://en.wikipedia.org/wiki/Dihedral_(aircraft)
While wikipedia isn't always a great source, the article at the link does a decent job of explaining how the dihedral effect works, and the distinction between dihedral angle and dihedral effect. The illustrations are helpful.
Perhaps you should start at this point in the article
"Using dihedral angle to adjust dihedral effect"
and read from there. I think it will answer your questions, in particular figure 2.
Also, if you draw yourself a sketch from top view of the aircraft, draw one with the nose into the relative wind (zero side slip) and one with the nose cocked off slightlly, which is a non zero yaw (nose not aligned with relative wind). This may help understand the sum of the forces acting upon the wing, and their direction.
If I remember correctly, the act of slightly masking (via the fuselage) the wing in the direction being slipped into, whereas the wing being slipped away from is not masked, provides the difference in total force via air flow over the wing to make the difference in lift leading to roll toward the slipped towards wing.
Dihedral effect of an aircraft is a rolling moment resulting from the vehicle having a non-zero
angle of sideslip. Increasing the dihedral angle of an aircraft increases the dihedral effect on it. However, many other aircraft parameters also have a strong influence on dihedral effect. Some of these important factors are:
wing sweep, vertical
center of gravity, and the height and size of anything on an aircraft that changes its sidewards force as
sideslip changes
.
Memory fails, but depending upon the wing itself, a slight side slip may influence airflow over the wing in terms of increasing "span wise flow" which is not as effective in lift production as chord wise flow ... but I apologize, it's been a few years.