I am preparing for CSE 2021. But sir i couldn't afford coaching and test series. If I write previous year papers then how can i evaluate my answer. How can i know whether i am going on write or not. Sir please help me on this

There are many free initiatives that you can take advantage of. For prelims, you can use daily MCQs posted by websites like Insights, Forum and IAS Baba. For mains, you can do Insight Secure, IAS Baba TLP etc. Daily CA can be found at Civils Daily free of cost. Current Affairs analysis is available online by Byju, Only IAS and Rau on their YouTube channels. For full length tests, you can use open tests one-two months before Prelims which are free. Unfortunately, I don't know about any free Mains test series. If you can save up money, you can use cheap answer writing evaluation like that by IAS Network or Convert IAS.