Once 6th round councelling ends, and you get your final allotment letter, your college will publish in their website , what next to do for final admission process.
All further details will be published on their website.
Whether they want the student to come to the campus or not, how rest of fees are to be paid etc. Each college may adopt different ways to complete rest of formalities of admission.
There are freshers forum on social media created by seniors of many colleges. Advisable to search for them and join for guidance.
Best wishes