Studying in school. Even then, you might not be able to actually understand the language since you are only exposed to it in academic settings.
Duolingo which is super fun, but once again, you will plateu quick and struggle past ordering pizza at a restaurant.
Anki is a great tool used by many hardcore language learners. It is a flashcard app, you spend more time on challenging material, and less on what you already know. The problem are that you often see words out-of-context, so even though your vocab can be huge, you might struggle using it in real life.
Leap attempts to fix these issues. Inspired byStephen Krashen's i+1 input hypothesisit shows you video clips where you know all words except the word you are currently trying to learn. This means your brain will have a lot of context which means you learn faster. Moreover, since you learn with real movie/tv show clips, you will automatically pick up pronounciation and train your ears to hear and understand the language.