There are a few different ways to add books to your BookWyrm instance! When you can't find the book you're looking for, try these options in order -- it's better to import a book than to create one from scratch.
If the book you're looking for isn't available on your instance, there are a few different ways to add it. The best way is to import it from an outside source -- your instance can load books from other BookWyrm instances, as well as OpenLibrary and Inventaire. If there are no search results for your query, these sources will automatically be queried, and will show up with a button to "Import book". If there are local search results that aren't what you're looking for, you can click the "Load results from other catalogues" link to load more results.
If you found the book you want, but not the right edition, you can add another edition to the work from the list of editions. Click the link below the description that tells you how many editions there are (for example, "4 editions"). At the bottom of the editions list, there is a button to "Add another edition".
Once you've tried searching for your book, importing it from another catalog, and finding other editions of the book, you can add a new book manually. The link to manually add a book is at the bottom of the search page when external catalogs are shown. You can also navigate directly to /create-book on your instance.