Answer Writing Issue

this is my 3rd Attempt, I am writing mains this time, being my first mains, I am having a bad feeling that I haven't written a single answer, that now I realise that making it without any writing is very difficult

Actually I always Knew that I should write answers but I didn't, I think the major reason for my not writing is that I don't know how to start writing. I mean if I start writing paper of 3 hours, I am not able to complete the paper and this leads to Demoralization.  Has anybody faced this problem when starting to write answers. How did you solve it ?.

Any suggestion how you approached answering when you started it will be appreciated.

Its causing me a lot of pain knowing that I have read a  lot but all that is useless as I am not able to write it properly on papers which matters the most.

I have tried some Daily answer writing  where they post daily questions on topics, but that didn't suit me as it kills that main idea of writing 20 Questions at a stretch.