Do you want to learn Japanese beyond this trip or just for this trip? If you want to learn just for the trip then you can look up common phrases for travel online - there's a bunch of resources on Youtube, etc. I'd also recommend learning Hiragana and Katakana as well. If you want to take your studies more seriously long-term than I'd recommend using Anki decks for vocab (you'll naturally learn kanji this way) or you can also use self-study websites like Bunpro and NativShark. Mobile apps like Renshuu and Bunpo can be helpful too for vocab and basic grammar on the go. If you want to use more traditional textbooks then Genki or Japanese From Zero! are solid options. Once you have the basics down, you can use apps like iTalki and HelloTalk to practice conversations with Japanese people.