So in japanese there are 3 alphabets. Can anyone explain when to use which alphabet?

The three alphabets in Japanese are: Hiragana, Katakana, and Kanji. I will explain below.

Explanation:

Hey there! Okay, so Hiragana is the first alphabet you should learn, and Every native Japanese word can be made into this alphabet.

Katakana is for slang, or non-native Japanese words, such as European names/companies/etc. There are often slang words written in this as well like I said, some natives think it looks cool (younger gen of people).

Kanji is used for more complex words. Since a lot of Japanese words have multiple meanings, Kanji is used to differentiate between those words (Instead of using hiragana and having to guess the meaning!) It's very important to know Kanji if you plan on learning Japanese, so make sure you don't skip out on it!