I'm trying to backup stock recovery topic

I am trying to learn how to back up stock recovery. I've searched Google and xda for the proper way to back up my stock recovery it sounds like I should be using ADB but it's been a little confusing reading all the post. Some say you need the custom recovery but if I flash a custom recovery how will I get a back up of the stock recovery. I would just like a reliable source to do this. my bootloader is unlocked I am S-off I am running software 3.31.651.2. any help would be appreciated.