BlueSky isn't launched yet, and Mastodon is horribly confusing. I'm glad they exist, and I hope they fracture the social media space to challenge the monoliths, but I'm not hopeful.
Threads will either fail like every other instagram spin-off or it will do the instagram thing where instagram copies an app and that feature is reasonably popular within Instagram but people still use the full service app version of the feature like how you can use Snapchat and TikTok within Instagram as Instagram stories and reels.
What part of Mastodon is confusing for you?
How do I know if I want to join an existing instance or create my own? What will I see if I create an account on one instance? How do I discover instances? How does federation work, exactly? Can I federate with an instance because I want to or is there some application process? What happens if I create an account on an instance but I don’t like it?