It's a multi-container application managed via Docker Compose.
I'm assuming you found the Docker Compose installation instructions here.

Essentially it pulls down the multiple containers required to run the site and orchestrates them for you.

I followed the installation instructions and got it up and running in about 30 minutes (I'm not sure why the theme looks slightly different; perhaps kbin.social is customized).
Right now I'm playing the waiting game to see if it eventually connects to other federated servers.

Let me know if you have any specific questions and I can probably point you in the right direction.