Some students apply to grad school before finishing undergrad. My husband was recruited into a GIS master's program by his then-current undergrad advisor. He was not required to complete any exams, essays, or interviews.
Often, work experience is required to gain admission. I started business school six years after college. I had to take the GMAT (specific to business), write essays, get recommendations, do a presentation, and be interviewed.
The GRE is a common exam for grad school admission. Other exams include the LSAT for law school and the MCAT for medical school.