There are many guides on getting started with Linux servers as a whole. I recommend installing Debian Bookworm on a virtual machine or a spare laptop at first and going through the writeups all major cloud providers have, just to get a feel for using the terminal & initial setup (SSH hardening and reverse proxy configuration and so on)

After getting an initial feel for Linux admining, start reading up on Docker, Docker Compose, and containers in general. Avoid Podman until you're experienced with Docker as it's just different enough to trip you up. You can also check out LXC/LXD although it's way less popular.

Oh, and speaking of Docker: UFW AND DOCKER WILL NOT WORK TOGETHER! DOCKER BYPASSES UFW (just making sure you don't learn this until it's too late)

Be careful of guides that are old (even a year makes a difference) or for different "distros" than the one you have. An exception for the second case is the Arch Linux wiki, which is one of the best resources just in general, aside from a few Arch specific bits like the exact package names to install. You should also use Arch's "man pages" reference, as they're built from the latest versions of packages compared to other man page renderers that are frequently outdated (like die.net)

Lemmy itself is harder to get right because the instructions so far are intended for people who kinda know what they're doing, but once you have the base Linux admin knowledge, it won't be that hard to pick up the parts necessary to get working with something like Lemmy.