its more an self hosted service,
Like if you host an lemmy server, you can also host faircamp to share music with, accross your lemmy's instance.

imagine my fake domain www.eikichithefrench.com,
i can use my main domain as an portal with an static webpage wrote in html, where you click on "lemmy.eikichithefrench.com" or "faircamp.eikichithefrench.com"

Sorry, my english, as u know now, im french,

I'd probably suggest having a dedicated machine. You don't need anything fancy, I'd imagine any old laptop should do.

It's essentially software to convert your machine into a basic web server, so if the laptop disconnects now nobody can download your stuff. And I assume you don't keep your laptop on 24/7

You'd probably want to host it on an actual server, if you want people to be able to access it when your laptop isn't on. The documentation seems pretty good, though, it should walk you through the steps: https://simonrepp.com/faircamp/manual/installation.html

If, and this is a big if, it can support an RSS feed that also allows you to provide the requisite info apple et al demand (3000x3000 pixel image, categories, etc.) then it could in theory support it. The bigger concern is traffic - will they be cool with you syndicating out and having folks pulling that frequently and can it support a lot of folks with larger shows doing it. Some podcatchers won't care and will let you just use an RSS pointing at the page hosting the files, but it's not a given especially with the larger ones.

My advice? Unless you want to really hack it together yourself and accept that it could force you to migrate without any notice, sure give it a shot. If you are risk averse, don't want to disrupt your listeners, aren't really comfortable doing a lot of tech troubleshooting, etc. I'd say don't try it. Podcast hosting is trivially inexpensive and all the big services have an embeddable player now if you really want folks to listen on your site.

Edit: worth noting that a lot of this is going to depend on whether an instance admin specifically wants to deal with all your traffic, assuming you get regular users/the numbers are decently high. If you stand up your own instance then it's all about what your infrastructure can support.

Yeah, everything you said there is correct.

If you want a somewhat more comprehensive definition:
Funkwhale, Lemmy, Kbin (as well as Mastodon, PeerTube, PixelFed etc.) are pieces of software, which can be hosted on a server and which implement a communication protocol for the federation of social media content.

If someone then takes such a piece of software and actually does host it on their server, then that's called an instance. Generally, they need to buy a domain name to do so, like "open.audio", "lemmy.world", "feddit.de" and so on.