Without beating much around the bush let me get straight to the point. The UPSC exam is a 3-phase affair:

Phase 1 is the UPSC Preliminary Examination, also called UPSC Prelims. This exam contains questions of the objective type.

Phase 2 is the UPSC Mains Examinat1ion, also called UPSC Mains. This exam contains descriptive-type questions.

Phase 3 is the Personal Interview round conducted to test the Personality of the Candidate.

With that being the case, I will now start off with the first part of the article which is the UPSC prelims syllabus.

To give you a brief about the UPSC syllabus, let me tell you, the IAS syllabus comes along with the official notification of UPSC CSE. While there are three phases adjoined with recruitment, the syllabus is defined for only two stages, the Prelims, and the mains.