On this page of the guide, you'll find out whether knowing the previous parts is required before starting God of War Ragnarok.
God of War Ragnarok is the ninth installment of the hugely popular God of War series and also a sequel to 2018's God of War. You do not have to know the story of the previous installment before firing up GoW Ragnarok, however, it is highly recommended.
God of War Ragnarok, as a continuation of the previous part, refers to earlier events, so playing the latest installment without knowledge of the previous one may confuse players a bit. From the God of War Ragnarok main menu you can watch a brief summary of the events of the previous installment, but it's much better to look for extended footage online or play it yourself .
It should also be noted here that God of War Ragnarok will conclude the Norse saga.