Found another nice page for reference. You might be able to get some explanations for the general operation of the network and instances, etc.
https://blog.soykaf.com/post/what-is-pleroma/
"In my last few posts I talked a bit about Pleroma. Since then, we had a lot of questions about what Pleroma is, how it is different from GNU Social and Mastodon, why you should use it and so on. This post will be an introduction to Pleroma, so read on if you are interested.
What is Pleroma?
Pleroma is a microblogging server software that can federate (= exchange messages with) other servers that support the same federation standards (OStatus and ActivityPub). What that means is that you can host a server for yourself or your friends and stay in control of your online identity, but still exchange messages with people on larger servers. Pleroma will federate with all servers that implement either OStatus or ActivityPub, like GNU Social, Friendica, Hubzilla and Mastodon."
Finished reading the page and it's excellent.
The author defines well what a Local timeline is, what the Federated timeline is as well.
And he explains the differences between Pleroma and Mastodon as server software alternatives:
"## How is it different from Mastodon?
If you are currently using Mastodon, you are probably interested in the differences between Mastodon and Pleroma. Here are some of the big ones.
## Lower system requirements.
Pleroma can run well on a Raspberry Pi or a $2.50 Vultr instance. This makes it affordable to host for single user instances. You can still run a hundred users or so on instances this small, though, so it also works well for bigger instances.
## Less moving parts.
Pleroma is built on a lot less technology than Mastodon. To run a Mastodon instance, you need Rails, PostgreSQL, Redis, Sidekiq, NodeJS and - if you want search - ElasticSearch. For Pleroma, you only need Elixir and PostgreSQL, while still getting all the features. This simplifies installation and makes maintenance somewhat easier."
original page (also linked above):
An example of a working, lively instance with Pleroma running. Showing their Local feed.
I support switching to Pleroma if it's cheaper to host, more efficient, and less complex on the backend.
@togs I liked that page too, and the low requirements, specially for someone considering running a small, personal instance in a home server.