Drupal 8 confusion

19:36:33 <wizonesolutions> So I am trying to convert the FillPDF admin overview forms from D7 to D8. They look like this: 1) http://i.gyazo.com/3293d9bc89e47cfe1de6d6ec2932e551.png (overview) and 2) http://gyazo.com/a0f9b32b124e1ee04c9de340a4b84b2e (editing individual PDF form). There's more to them, and the screenshots are a little out-of-date, but it gets the point across. So
19:36:33 <wizonesolutions> anyway, my point: c_hx said I should use fields instead of using a database table to store these, but I am still not quite grokking the correct approach. p_enyaskito pointed me at Field Items, but it doesn't seem like this is *quite* that. That seems more like when you want to define more custom stuff, or attach something to something else (e.g. comments to
19:36:33 <wizonesolutions> nodes). But really I'm essentially letting the user record information that is connected to the files they uploaded, which conceptually is a "FillPDF Form." So I'm thinking, maybe that's an entity that extends File somehow and by default has some common field types attached to it, and I have to use the functions for creating entity forms to make the form for
19:36:33 <wizonesolutions> editing an individual one? Still wasn't really sure. Right now I just use a database table to store that info and join it on fid.