How to join big IT companies after graduating from an engineering college?

Prepare your resume and apply in every company for your domain, wait for the callback till then study and get ready for an interview. Work on communication skills if you lack in it.

There are two concepts in your question that need to be properly understood. One is Job and the other is MNC companies?

Let's look at the concept of a 'job'. What needs to be emphasized is that a job is a mutually agreed legal relationship between two parties, of which one is an individual while the other is a corporate entity. From your perspective as an individual, you need to be clear what type of relationship you want to get into. It must also be clear to you that not all companies offer the same type of relationship. 

Next: what is a MNC? (I hope you realize there is no need to call it a MNC  company, because the C refers to a company). A MNC is an organization that has deliberately decided to extend its activities  across borders. this means it has to operate under different cultures, regulations and expectations. Thus, a MNC will prefer to hire people, ie get into relationships, who can help them to cope with this varied external environments. So, if you want to enter into a relationship, ie land a 'job' with a MNC, you have to convince them that you have the desired skills and competencies. 
How do you find out what are the desired skills and competencies? By doing a lot of homework and legwork. When I wanted to join HUL, I got hold of their Annual Reports of the last 5 years and went through them thoroughly. Then I found out people working there and went and met them. Only after I was clear what they were looking for did I approach them.

So, prepare yourself thoroughly and then only you can succeed. There is no easy and free lunch in the harsh world of corporate life.

Thanks and stay blessed !