Reed
I think they mean account-scale points. As in the 30 points you get from this post and 20 from a different post total to 50 karma. Pretty core feature on Reddit and doesn't exist on Lemmy.
You can't login to other instances because you don't need to. And also they don't have your login credentials (what a mess that would be). But all the content from that instance is already available to you on your homepage and you can comment on it, up vote it... Why would you want to?
Instance and server are interchangeable. Instances have multiple communities, as many as you want. Beehaw instance only has like 20 while Lemmy.world has hundreds. Starting a community on an existing server is filling out a form, basically signing up for a website. Starting an instance requires hardware, metal or cloud, some experience with server software and command line interfaces, and patience. Any Lemmy server can federate with all other servers so you can show up on my feed when I hit "all" instead of "local." You can be defederated with for technically any reason by any server. It doesn't happen often outside of beehaw and most of their defederation list is like Neo Nazi shit.
I hope those outrage porn subs don't make their way here. If people want them it looks like Reddit will be open for a while longer. But I feel like it's too toxic to have on Lemmy.