Hi Abhishek,
if you want to take admission in centralized courses like BCom, BSc, BBA,BCA, etc. then you need to fill the online centralization admission form. The colleges will be allotted on the basis of this form. Although you may change your college in rounds of counseling. The students not filling that form are sometimes not qualified to take admission in centralized courses in colleges affiliated by PU. The form will be most probably released soon in first week of June. It will be updated on following website:-
http://dhe.chd.gov.in/DHE/index.aspx
Keep checking this website. You will also be provided with whole admission procedure and datewise schedule of whole process on same website.
Keep checking latest updates.