I have figured out that I need a client, that I need to register at a server. And then I can join, read or participate in channels and take part in the conversation. Is that right?
Pretty much, yeah. The "standard" client is element
, which is usually the first to implement new Matrix features. But as it's chonky and doesn't integrate well with some desktop environments people also use alternatives like e.g. nheko
For that matter, does it matter what server I chose for registration.
I'm just using the default matrix.org one until I finally set up my own.
Can I join any channel with an account on whatever server?
Should be the case, unless there are server-specific bans in place.
How do I chose the right server for me?
If you have no intention of setting up your own, and no specific reasons to use another one, just use the matrix.org one IMO