Honestly, you don't need to "learn" or "understand" much grammar explicitly. I think it definitely helps get you off your feet, as you can "decode" sentences if you remember grammar rules, but eventually the grammar has to be internalized anyway. This happens when you are repeatedly exposed to the same patterns in context. I don't know how English or Norwegian grammar works, and I'm fluent in those. I skipped grammar in Japanese and focused on reading, yet I can understand most things and I can tell when something sounds wrong.