A spherical lens in its simplest form is the magnifying glass. This lens is convex on both sides, and those faces are shaped like sections of spheres. The strength of the lens is described in diopters. A spherical lens that is convex on both sides is a "plus" lens, and is used to treat hyperopia. The next type of spherical lens to know is the simple minus lens, which is concave on both faces, and is used to treat myopia. Most opticians produce minus meniscus lenses, which are convex on one side and more concave on the other, resulting in net minus power.
Spherical power is the easiest to reduce when adjusting your lens selections. You can use a cm measurement (duochrome test recommended for cm) or Snellen chart test to determine when you're ready to reduce power.