you just load your books from Calibre (or right through USB if you’re hardcore for some reason) and you’re basically off to the races.

There’s also an OPDS server option with calibre-web that you can use to load books from if you’re using koreader.

You can also use the Kobo server replacement option with calibre-web although I personally couldn’t get it to work at the time I tried it. But this will give you a sync option that works like the official Kobo server which is quite nice.