you should buy the book or you also download from website which name is Mina no nihongo (I) in oder to start learning Japanese. Hope you will enjoy learning Japanese.

I would recommend start learning the hiragana first because every book or course will start you with that. Here are beginner Japanese series. -Japanese from Zero -Genki -Minna no Nihongo -Human Japanese -Japanese in Mangaland I would recommend you choose one of those series, but look at samples or previews for them to decide if it is right for you.

I'm no expert at this since I'm still starting but many sites recommend to start learning hiragana first! Then perhaps katakana and etc.