FBM vs FBA for an eBay reseller

Can anyone please explain how FBM works? Shipping, pricing, etc

I am doing ok on eBay as a pure side hustle, but I’d like to cross sell on Amazon, but obviously I can’t mail it in if it’s listed on eBay.

I’m mostly used books, video games, DVDs and 1 console in my inventory a used ps2

Is there anything in those categories I am better off to just go right to Amazon FBA with? Starting to run out of room in my house for inventory,

I do have a lot of free mass produced books that are part of my inventory