Disy
It's a big form so I can understand why you are finding it so intimidating. Try and break it down into smaller parts, so don't try and fill the whole form in, pick one question and try and answer that and if that is still too much then try and write some bullet points for the question, then when you feel you can, convert each point into a sentence and then into a paragraph, etc., if you get stuck on a question move onto another and come back to the original one later.
Have you looked at our PIP Claim guide, it explains what is being asked for each question, has a "formula" for answering and examples you can adapt to your own situation.
www.benefitsandwork.co.uk/help-for-claimants/pip Gordon