I want to learn Japanese, how to learn this language quickly？

New_Bumble_Bee's answer is fine, but costs a lot of money either way. And it does have its benefits like having a unavoidable schedule and listening practice.

But, the truth is. You can learn any language for free now. And how you want to. I've been learning for the past 2 years for absolutely free by downloading japanese movies/anime/etc, and dl'ing their respective subtitles or 字幕. That is great for reading comprehension, and listening. Also, i have been using lang-8.com to find study partners, and multiplayer videogames as well. Additionally, you can look up on youtube/niconico 実況プレイ videos for videogame commentaries^.^ If you find one you like, dl it. They get taken down often for reasons I don't know.

And another point. Not only is self study potentially free, it's also the quickest way to learn. I remember when I started, after about a month or 2 of self-study I watched youtube videos of people who took college courses for 2 years and their skill level was non-impressive.

The key is consistency and determination.

Ganbatte^.^

Watch anime, and listen to english and japanese pop music.

Go enrol in a Japanese 🏯 course in the local community college 🎓 - alternatively if you've got enough money you could always catch a flight to Japan 🗾 and hire a translator / Japanese 🏯 tutor though if you want to learn a subject properly it takes time ⌚