The first stage of the UPSC Civil Services Examination is the Preliminary Examination, often referred to as the "Prelims." This stage consists of two objective-type papers that test candidates' general knowledge and current affairs. The Prelims serves as a screening mechanism to narrow down the pool of candidates eligible for the subsequent stages of the examination, namely the Mains Examination and the Personality Test. Success in this stage is crucial for aspirants, as only those who qualify can proceed further in the selection process.