The way in which dihedral affects the angle of attack of each wing can be demonstrated using a simple sheet of A4 paper or card.
Fold the paper over so that the two short side are together and a crease is formed down the centre. Now unfold it so that it takes up the shape of two wings with dihedral. The crease represents the fuselage and the the two halves of the sheet represent the wings.
Now close your left eye and hold the paper about 18 inches in front of your face, so that the crease points directly at your right eye. In this position the end of the crease closest to your eye represents the nose of the aircraft.
Now raise the nose to give it a slight pitch up attitude. This position represents an aircraft flying directly into wind, with no sideslip. Now imagine that the wind is blowing from your right eye towards the aircraft. This means that the view from your right eye represents the view that the air gets as it approaches the aircraft.
Looking with your right eye you will be able to see the underside of both wings. If you look carefully you will observe that your views of the two wings are identical. This means that the angles of attack of the two wings are identical.
Now to represent sideslip turn the paper slightly so that the crease is pointing towards your left eye. Looking once again with your right eye you will see that your view of the two wings has changed. You can now see more of the underside of the wing that is closest to you and less of the underside (or possibly even some of the upper side) of the wing that is furthest away from you. This means that the angle of attack of the closest wing has increased and the angle of attack of the furthest wing has decreased.
The greater the degree of dihedaral and/or the greater the angle of sideslip, the greater will be these changes in angle of attack.
Now turn the paper over so that it represents anhedral and repeat the experiment. You will see that anhedral has exactly the opposite effect.