Sorry if this has been asked, but how do I find and subscribe to communities if no one on my instance has searched for it yet?

I cant search for some communities that show up in newcommunities, and I hear that thats because no one on my instance has been to them yet. Well, how do I be the first one? I cant join by searching because it wont show up, and if I click on a link there it takes me out of the app to that communities instance, and logs me out, and I cant log in because I only have the option to log in to their instance which I dont have an account on.