Candidates are selected for the IAS after the UPSC exam through a rigorous three-stage process: Preliminary, Mains, and Interview. The Preliminary exam consists of objective-type questions that test general studies and aptitude. Successful candidates move to the Mains, which includes descriptive papers covering various subjects. The final stage, the Interview, assesses a candidate's personality, knowledge, and suitability for civil services. The combined scores determine the final ranking, ensuring a meritocratic selection process for public administration.