I just know campus interviews are done and students get the job. Now its my time to face it so I want to know what is it about? Like when do the companies come for our colleges, what are the primary stages of the interview? How should we respond?

Often the whole process is done in a large open room, with tables and panel dividers, a job fair.
You walk up enthusiastically, shake hands, and tell the person your course major and main interest. You sell yourself, you don't wait for them to ask questions at first. You are the best person for their company because of all your good grades, your thesis, your projects, professors you worked with, and your special area of interest. You plan to do graduate courses one at a time after the first 2 years, etc.
Then you wait for them to ask you questions. They often end with 'Do you have any questions for us?' Ask about R&D, expansion, financial situation, stock options, benefits, advancement, etc. It wouldn't hurt to read their website before you approach, or do even more research.
Of course you hand them your resume near the beginning, but it's better to tell them what's in it. Personal interaction is key. Unforced interest and enthusiasm are key. Look people in the eye.

I forgot another ingredient: you tailor yourself and your questions to the company.
A 5 person startup? You are willing to bring a sleeping bag to work and live on rice. You don't ask any of the usual questions you ask a big company except maybe stock options. You want to know all about their product and ideas and how you can contribute. A multinational corporation? You ask about locations, languages needed, etc.
Each company, a different approach.