Hello Siva,

Yes you have to compulsorily include language among the best four. It can be either English or Hindi, whichever you have scored more.If you're from Science stream, your main subjects would be Physics,Chemistry,Maths/Biology and English. If you're from Commerce, it would be English, Business studies, Accounts, Maths/Economics. If you have not studied language or not adding it you will have to reduce 5% from overall percentage.

https://university.careers360.com/articles/du-cutoff

To know how to calculate percentage :

https://university.careers360.com/articles/delhi-university-admissions-how-calculate-best-of-four-marks

All the best