N levels are the levels of the levels of the JLPT (Japanese Language Proficiency Test) exam. They go from N5 (most basic) to N1 (most advanced), and if you google something like "JLPT placement test" you should be able to find resources that will tell you your approximate level if you want.
JLPT levels are used in relation to a lot of Japanese-learning things because it has a monopoly on language testing, not because it's actually a useful system or accurately describes anyone's competence with the language. It's not necessary at all to use JLPT materials to study or to measure yourself against JLPT levels if you don't plan on imminently taking the test.
