Hello,

The admission in IIST is based on merit in JEE Advanced.Candidates who have qualified in JEE Advanced can register for IIST admission after the releasing of notification.Once the registrations are completed a rank list will be released, candidates who are in the rank list can opt for branches by logging with their credentials in official portal for admission.The choices need to be locked.Based on the preferences candidates will be alloted branch, candidates can accept the seat and freeze the allotment if they are satisfied.After this they need to report at the centers for fee payment and verififcation of documents and admission will be given.
You may refer the article for which the link is given below

https://engineering.careers360.com/articles/iist-btech-admission