What are N4 and N5?
N5 is the first step: you can read hiragana, katakana, and about 100 basic kanji, and understand simple everyday conversations spoken slowly.
N4 goes one level further: around 300 kanji and 1,500 vocabulary words, with the ability to follow daily conversations and read simple passages.
Together they form the foundation you need before progressing to N3 and the N2 level required by most Japanese universities.