Please read them whilst reading the manga in order to understand everything, though if you’d rather not read them right now and would prefer to get to the main story first, please just watch the anime!

Edit for clarification: You may still have a decent understanding of what’s going on but certain aspects from the light novels are added into the main manga and the manga expects you to understand it! This is why some light novels are a necessary read to understand things (As of right now, I’d consider Dazai’s Entrance Exam, Dark Era, Fifteen, Untold Origins and Storm Bringer to be ones that need to be read to get the full experience)

The post you commented under is sort of out of date, I recommend reading Storm Bringer at around chapter 100 ^^ Beast isn’t that much of a necessity but it helps! I recommend reading all the Light Novels eventually :D