Lemmy

Can I only create a community on the instance I joined, or can I also create a community elsewhere?

You can only create a community on the instance you have an account on, but people from other instances will still be able to follow and post to it.

You can only start a community on the instance you joined. As has been pointed out, people from other instances can still interact with it.

You don't really need any guide, it's super easy to create a community, just hit the link at the top of your page. Give it a name (this will be its address, and can't be changed, so your community would be name@feddit.de) and optionally a display name. You can also add an icon, a banner, and a bio. After that, you just have to start sharing your community and regularly posting.

As of now, community numbers are small enough that I imagine any moderation work to be extremely minimal to non-existent.