Hey there!
yes you can apply for BA.LLB course in calcutta university. But for any law colleges, except NLUs that have CLAT, you have to give separate exams that the university itself conducts keeping in mind the cut off they determine. For Calcutta University, they do not take any entrance tests for this course. The applications are welcomed till 20th july for this year and the merit list will come out on August 12th 2022. Note that the application is taken based on your hsc result.
Wish you the best