As the others imply you need to be more specific to get helpful answers. What grammar do you know? How much can you read? Do you have a native speaker (your parent?) around to help you? How much money are you willing to spend? Since technically "oishii!" is a coherent and grammatical sentence in Japanese, you probably can actually form some sentences...
You can always go to your local/university library to check for free resources. I do believe that the structure of a textbook can be really beneficial for self-study. I can't recommend a book without knowing your level though and "beginner" is too vague.
Basically my method when I was learning intensively and as cheaply as possible was a) go through at least one chapter of a textbook a week, making notes by hand b) brute force learning of kanji by copying them and their readings out (no one has yet convinced me their super-special memorisation technique is better) c) text chat with native speakers on LINE d) flashcards whenever bored or waiting for the bus e) watch a load of Japanese films and TV dramas with subtitles
I don't claim my method is the best or anything, but it does work.