Lemmy is the fediverse link-aggregator, like Reddit

Mastodon is the fediverse microblogging platform, like Twitter

On Lemmy you subscribe to communities, but on Mastodon communities are essentially hashtags, so you can also follow users to get updates directly

lemmy.world status according to this thread

I’m glad I went through that stuff in the demo, where I fully expected it. Jumping right into the main game a few days in was another huge bonus for playing the demo.