Ohh gotcha! So for going to other people's islands, I assume you're talking about ACNH (animal crossing new horizons), so for that you would head to
The Airport and there you can see people hosting games or looking for people hosting games for purposes such as getting items, giveaways, hang out sessions, etc. Myself I never use that, but sharing a friend code or dodo code would both work. Camp Bell Tree is a competition type of event going on that is somewhat related to animal crossing in the sense that some of the tasks involve the game (I don't know if I'm allowed to disclose them), but it isn't sponsored by Nintendo or anything of the sort, it's just a way to engage with TBT's users and for the chance to win collectibles for the site.
If there is anything else you need to know, please, don't hesitate to ask!