To explain federation (I am terrible at explaining things),

Every user/group on an instance has an inbox and an outbox, for example, yours is lemmy.world/u/Docker@lemmy.world/inbox and !nostupidquestion@lemmy.world’s is lemmy.world/c/nostupidquestions/inbox .

When a post is made, its sent a group’s inbox, and then the group sends it to the inbox of every user subscribed to it. If I send you a direct message, my server sends it to your inbox.

If you go to a post in your browser, it shows it in the web interface, but if you set whats called a header (some small bits on information sent to a server when you request a page) saying that you’re a server, it gives you a machine readable representation of it.

For example, your comment here looks like this:

{
  "@context": [
    "https://join-lemmy.org/context.json",
    "https://www.w3.org/ns/activitystreams"
  ],
  "type": "Note",
  "id": "https://lemmy.world/comment/17178560",
  "attributedTo": "https://lemmy.world/u/Docker",
  "to": [
    "https://www.w3.org/ns/activitystreams#Public"
  ],
  "cc": [
    "https://lemmy.world/c/nostupidquestions",
    "https://startrek.website/u/FriendOfDeSoto"
  ],
  "content": "<p>In this regard, can a singular website function like a unique instance of the fediverse ?</p>\n",
  "inReplyTo": "https://startrek.website/comment/16837450",
  "mediaType": "text/html",
  "source": {
    "content": "In this regard, can a singular website function like a unique instance of the fediverse ?",
    "mediaType": "text/markdown"
  },
  "published": "2025-05-21T09:55:42.214962Z",
  "tag": [
    {
      "href": "https://startrek.website/u/FriendOfDeSoto",
      "name": "@FriendOfDeSoto@startrek.website",
      "type": "Mention"
    }
  ],
  "distinguished": false,
  "audience": "https://lemmy.world/c/nostupidquestions",
  "attachment": []
}

So, you could make a post or page of a website like one of these, and then manually send it to everyone’s inbox, but you won’t be able to handle incoming messages.