You go to a company saying "we sell your wares on Amazon.com," and sign a contract. Your goods come in from one end, cash comes out on another.

Usually that's all

If the guy sucks, you go to another one.

You can see a company called Ugreen, which ended up with multiple "official stores" on online marketplaces this way.

Contract enforcement in China is of course non-existent. It's good if you manage to get a prominent handle for your own brand, in worst case somebody else can do it for you!

I know a man who regularly have to smack pretender "official stores" of his brand few times a year.

This also works the other way around, somebody with a vicious lawyer can coerce Alibaba, or JD into handing your (likely well doing) online store to them on a claim that you don't own your own brand name.

Factories aren't on Ali. English speaking businesses that but from factories are.