Not sure how I got to lemmy.one but when it said I had to login to comment on something, my userid/pwd that works here didn’t work and the registration link said user registration is closed. Aren’t lemmy logins supposed to work across the whole federation? Or are there multiple federations and lemmy.one is entirely different? Maybe I misunderstand the whole scheme of lemmy.

edit: Okay, after a little experimentation I think I get it. On the domain lemmy.world, when logged in, if I look at a thread I see the comment box, but if I go to lemmy.one and find the same thread it says I must login to comment. With the explanations everybody gave here, this makes sense now. So thank you very much, I appreciate the help!