an ELI5:

When you set up a lemmy instance, it has no idea other instances exist. It's like throwing you into a web browser with no search engine. You don't immediately see every single website, you have someone tell you about a cool website you found, and then you type it into the address bar, and save it.

It's kind of the same thing with Lemmy instances and communities. Once a user types this syntax into the search prompt:

[[email protected]](/c/[email protected])

It will try and contact instance.com for that community. If it exists, the user can subscribe and the instances will now receive and send new posts to each other.

What does it mean “fetching communities on my home instance”?

This is actually bad for the instance. It costs a lot more resources to send and fetch submissions from a bunch more instances.

I am sure more knowledgeable people will provide the right answers. But I think it means that when you set up your own lemmy instance, you need to add the communities to it.

A real Stakhanovite of the fediverse!