Lemmy is community-centric like Reddit, rather than user-centric like X/Twitter. If you want to follow specific users then look for a microblog platform like Mastodon. Or try mbin, which combines multiple platforms as another commenter mentioned.
You can only subscribe to communities on Lemmy, no individuals. For individuals, you'd want to use Mastodon (twitter-like) or Mbin (Reddit-like with Twitter-like abilities).
If you're new, I'd recommend installing Instance Assistant, then searching for communities that interest you either organically from your All or Local tabs, or searching across all instances with Lemmyverse.net
Nope, you subscribe to communities like subreddits.
Subscribe to communities that you like, subscribe to similar communities from multiple instances. E.g. there's News in more than one. Then set your feed to Subscribed and sort by How, Active or Scaled (perhaps best). When you want to see what's going on elsewhere, switch your feed to All + Top, or All + Hot / Active. If you want to discover small communities you don't know about - All + Scaled.