How do I add a full screen landing/hero graphic?

Hi . New here. I’m looking to make a sort of landing /hero image that will take up the full display on my website. I would like it to cover everything including the header. So once you scroll the image slides up revealing the real home page. Once that image is gone you can use the website like normal and it doesn’t return until you reload the home page. Any ideas on how to make that happen?