Originally Posted by charlie94
...so in theory (networking geek hat going on) if I had html/htm and wanted to drop not only the htm file but the folder with all the images in it as a zip file, into Calibre I could?
You can zip all the constituents (html, css, images) into a zip before importing into Calibre if you want but it is not necessary. If you just drag the html file Calibre will find all other referenced files and zip them up during the import.
Similarly, FYI, if you have one of those ebooks which is made up of several html files (e.g. 1 per chapter) plus a "master" index or TOC html file then you only need to import into Calibre the toc.html or index.html. Once again Calibre is clever enough to follow all the links and will zip up all the individual html files during the import.