Sculpt mode is used to perform basic sculpting operations. By default, the mesh will be displaced in the direction of the 'average normal' of the vertices that fall within the brush radius.
By holding the SHIFT key, the mesh will be displaced in the vertical direction only.
It is recommended to use a relatively small strength value (10%-20% of the radius value) and gradually deform the mesh through successive brush strokes. This will provide smooth deformation and greater control.
A negative strength value (strength indicator points towards the mesh) will result in the mesh being deformed in the opposite direction.