One of the options under the connect/share button is “Start content server”. Then you can access that page in a browser on the ebook.

Calibre just provides a little management on top. I use it for doing things like cleaning up metadata (making sure all books in a series have the same series name, for example), and transferring books over wifi (calibre can spin up a mini web server that I can access on the kobo).

I could get by without it, but it’s nice sometimes.