Is it normal that I would NEVER have found those great articles without the direct links provided in this comment? I've been using Duolingo for almost a year now and have never ever found any access point for browsing articles on grammar. Only exercises, comments and settings. I use both web and android versions of Duolingo.
Keep in mind that most DL sentences have very little context...so it forces you to think of a context each time. I think that is great because it actually makes you think rather than gives you a quick answer or fix. Some of these sentences make me think of a foreigner who would say something correct in Italian but not grasp the full meaning/implications of his own sentence.