Marbles, oranges, bubbles, and beach balls — all of these objects illustrate the shape of a sphere, or globe (unless the beach balls are under-inflated, in which case they’re sort-of a “squished-sphere” shape).
Sphere is often used metaphorically to refer to a particular aspect or area of something. For example, unless you’re a trained circus performer, tightrope walking and fire swallowing probably lie outside of your sphere of expertise. Sphere frequently occurs in the phrase “sphere of influence,” which designates the geographical area over which a person, organization, or nation has control. In many households, whoever is in charge of the cooking controls the kitchen; so, the kitchen falls within his or her sphere of influence.