Verony,
It would be really helpful if you can mention what exam/college/university/etc. you are referring to. It would be really helpful for us to answer.
If you're referring to Delhi University CET, then I would say there is no compulsion for joining coaching centres. YOu can freely prepare on your own. It would majorly focus on Commerce subjects of +2 and Maths as well.
For more on the same refer to:
https://university.careers360.com/articles/du-bcom-application-form
https://bschool.careers360.com/articles/du-jat
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