UPSC application is separate for both IAS prelims and IAS mains. IAS prelims application is open for everyone.
Check the eligibility criteria for the IAS exam before submitting the UPSC online application form. Next, candidates who clear IAS prelims have to submit a detailed application form for IAS mains.
You can only apply for UPSC exam through online mode, UPSC will not consider any offline civil service application through postal. Also, you have to apply for civil service through UPSC official website.
UPSC specifies the IAS application starting date, IAS application closing date and other IAS exam details in UPSC exam official notification. It is mandatory to submit the IAS application before the last date mentioned by UPSC.
Usually, UPSC gives a month duration for IAS application submission. There are two parts in UPSC registration process
UPSC Registration part I: Input your personal details, contact details UPSC Registration part II: Scanned document upload, mode of fee payment, choice of exam center