Hey Soumik!

To apply online for an eligibility certificate,the process may vary a little depending on your state/board/University.But in general here's how you can apply it:

•Visit your official University/board website

•look for eligibility certificate/admission service or relevant section

• fill out the application form with your academic details

• upload the required documents like Marksheet,TC, passport size photo etc.

•Pay the prescribed fee and submit the form

Once submitted you'll receive an acknowledgement or receipt,and later the eligibility certificate will be issued online or sent to your college.