If we’re offering resources for unknown phrases (I say phrases, and often times vobulary, rather than foundational grammar, which you might be better off learning formally from books or learner-oriented sites), and aren’t equipped to dive headlong into native-oriented language resources or want to check translation precedent, you can’t do better than https://ejje.weblio.jp/. Weblio is a Japanese-native-oriented two-way English-Japanese dictionary that–and this is by far its best feature–aggregates example sentences from real translations. In my own translation practice, that’s been an extremely useful tool. No machine algorithms; just a bunch of examples of how real people have handled certain phrases in pubished examples. The only drawback is that it might require a better handle on Japanese so you can actually parse what’s happening between the original and translation. As such, I’m not exactly sure how truly beginner-friendly it is. Still, I think it should be able to help you get more a practical gist of new phrases. (That said, there’ll be times, especially in more colloquial manga, where only searching for explanations in Japanese aimed at natives will do.)
If I’m just looking up an individual unkonwn word that pops up while reading manga or prose, I just use an En<->Jp phone app or Jisho, though, definitely. If I’m translating something, I’ll check weblio and native language resources to makes sure I have a stronger handle on it.
I add new words to decks on Quizlet (substitute with Anki or the digital/physical flashcard system of your choice), but that isn’t something I would have bothered doing for every single look-up prior to passing N2. For one, it would have been too time-consuming, and for another, it wouldn’t have been a good use of time as I continued through foundational/test-specific vocab lists.