The Civil Services Preliminary Examination consists of two objective papers and serves as a screening test, while the Main Examination includes nine descriptive papers assessing candidates' analytical abilities, knowledge, and understanding of subjects. The Prelims tests general studies, including current affairs, while the Mains evaluates in-depth understanding with subjects chosen by candidates. Additionally, Mains includes an optional subject and an essay paper, emphasizing writing skills and comprehension. Candidates must clear the Prelims to qualify for the Mains, which ultimately determines selection for the interview stage.