The syllabus for the UPSC Prelims focuses on general studies and includes objective questions testing comprehension and analysis across subjects. In contrast, the Mains syllabus is more comprehensive, requiring descriptive answers that demonstrate depth of understanding and critical thinking. The Mains exam includes subjects like essay writing, optional subjects, and various papers requiring a detailed exploration of topics, rather than just recognition and recall from the Prelims, emphasizing analytical and expressive abilities.