Right. When I go to my "kindle content" the books have no titles, just numbers.........I usually go by date to see which one I want to import.
Just click "add books", on Calibre, then click on any file and when it is imported, if you have the plug ins installed correctly, the book will load with title, and cover, if provided, drm free.
If there is no cover or synopsis, you can then choose "edit metadata" on Calibre and it will find the appropriate info for you.
After all that is done, you can choose "convert books", choose 'epub' from the menu on the top right, and you're done.
All books can be converted at the same time if you like.
Once all books are loaded, I just delete them from the Kindle content file......they are always reloadable from Amazon, and it keeps the clutter down.
edit: this is just my way of doing it.......as noted, there are others!