Hy lakshmi!!
The admission process for most of the colleges will begin after the declaration of 12th result as they will decide the cut-off only after the declaration of board result.  For some colleges it has already been started as they have made their forms available for the entrance exam. The process of Admissions will go on till july- august. You should keep a look at the forms coming for the admission so that you do not miss any form.
The admissions in under graduate course is entirely done on the basis of your 12th percentage in government colleges. However, you can get some kind of counseling during this time regarding which course you should take.
All the best!!

Hey,
Usually in May, online registration gets started.
But u need to be more specific about your query
About which college you have want to know the admission dates.

Thank you