Three basic hair cuts
One length (bob)
In its purist form it is cut completely on the outside shape / edge. Weight and fullness on the outside shape. The whole shape of the cut tends to look triangular, i.e.. more width at the bottom edge than anywhere else.
Starting at the nape, take small sections from the hairline and cut a guideline. Using your guideline take small sections from the back and cut parallel to the guideline.
Starting on one side of the head, and using the previous guideline, take a small section from the hairline near the nape and cut a new guideline following on from the previous guideline. Using your new guideline take small sections from the side and cut parallel to the new guideline.
Do the same on the other side. Getting the client to move their head slightly from side to side and back and forward will show any signs of unevenness between each side.
A fringe can also be cut in the same way by cutting a guideline along the hairline at a suitable length.
The hair is cut all over the head at varying angles following a guide length , this creates a lot of inside shape or movement. Weight and fullness is evenly distributed. In its purest form the whole cut tends to look round and even.
The hair is cut and held away from the outside edge, reducing weight and fullness on that edge and moving it to a higher line. In its purest form the whole haircut tends to have a diamond shape, i.e.. wider in the middle than anywhere else.