To apply for the Sub-Inspector (SI) position in Delhi Police, candidates need to visit the official website of the Staff Selection Commission (SSC) and complete the online application process. This involves One-Time Registration, followed by filling out the online application for the examination. Applicants must carefully read the instructions provided in the Notice of Examination, have necessary documents ready such as mobile number, email ID, Aadhaar number, educational qualifications, and a scanned signature. After logging in with the registration number and password, candidates can proceed to apply for the SI position by following the detailed steps outlined on the SSC website.