Many means can be used to learn a language:
- classic textbooks,
- language schools,
- private teachers,
- (multi)media courses,
- web sites,
- movies and subtitles
- audio or video player with functionalities for languages study (soft subtitles, A B repeat)
If you are in a hurry to buy something and start learning Japanese you may go here, in the amazon language store. We do not recommend doing this.
If you are not in a hurry probably it would be better to think well about
- your objectives and motivation
- what type of learner you are
(ex. which of your memories works best? can you study long hours alone or that depresses you? ... )
- how much time you have to study and in which environment (will you study sitting at a comfortable desk or while commuting? ...)
After that read as much as you can about study methods, read product reviews (not advertising disguised as review) then choose you method as carefully as possible.