My LRC library is a mess. Is it possible to delete all library details and start again from scratch? Obviously I am new to LRC and have blundered in where other people would not have. Thank you.
Yes, you can create a new catalog.
Here you'll find Lightroom Classic tutorials: https://helpx.adobe.com/lightroom-classic/tutorials.html
As stated, you can create a new catalog. Please be aware that when you do this, you could lose all edits and all user-provided metadata. It is better, in my mind, to fix the problems in the existing catalog, but that takes time and effort.
What problems do you have?
If you edited the images, or added metadata such as keywords, then do the following before you start again from scratch: Go to 'All Photographs', choose 'Photo - Expand all stacks', select all images (ctrl-A on a PC, cmd-A on a Mac) and then choose 'Metadata - Save metadata to files'. That ensures that your edits and metadata are automatically imported into the new catalog when you start again with a new catalog.
Side comment: Save metadata to files works only if the photos are in the location LrC expects; if there are ? icons on the folders or ! icons on the photos, Save metadata to files doesn't work.
It sounds like your photo organization may be a mess as well. LrC only mirrors your disk organization.
Before starting over consider reorganizing. I'd suggesting looking at the books, blogs and forums in the Lightroom Queen https://www.lightroomqueen.com/community/. I say this because I started from scratch with a new catalogue several years ago and now wish I'd simply reorganized.
If the problem is organization of photos, rather than just using LrC poorly or some other problems, see The DAM Book.
But the original question did not mention the exact type(s) of problems that the user was having; and so we have in this thread lots of good suggestions, each of which may or may not address the original user's problems.