I wrote another guest article over on the AuroraBits blog, going into some detail on each of the current  web parts (as of late September 2017 when I wrote it) for SharePoint Online Modern pages. Actually, there was so much material and detail that it turned into a two-part post, which I broke down by whether the web part displays static or dynamic content:

Part 1: Adding web parts to a modern SharePoint page, and static-content web parts

Part 2: Dynamic-content web parts

I realize that at this point things have already changed (for example, you can now create and upload files through the Document Library web part), but I still think these articles give a good starting point to using many of the new web parts.