The admission in colleges which come under Delhi University for the courses like B.Sc, B.Com, B.A are done on the basis of 12th merit and there is a centralized application form which you will have to fill up for the same. 

For reference, you can go through the below links -

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

https://university.careers360.com/articles/du-application-form

Good Luck!!!