This is a pleroma instance. It's social media, but a bit different to what you might be used to.

Register

If you have trouble with registration, contact me (or send an email to zerglingman, of fedora.email).

Once you've registered, you should get a client (an "app"†) and login with that. You can't sign-up from clients though.
Search in your favourite source of software (eg. "app store"†) for a "pleroma client", or a "mastodon client". Mastodon clients will work with pleroma instances (which sacred.harpy.faith is), but they'll be missing some features and functions.
I also recommend some clients, on the Q&A