Install Virtualbox (or some software to handle virtual machines).
Install Debian (or some other OS of your choice, I won’t judge if you prefer Windows).
Update your OS (apt update && apt upgrade -y on Debian).
Take a snapshot of your VM’s current state after updating. Saves a lot of time if you mess up or want a clean slate.

Now you decide on what you want. Do you want to install n8n or Node-RED for automation? Do you want to use Immich for pictures? Paperless to save papers in a digital format? Audiobookshelf to listen on your books or podcasts? Jellyfin to stream your media? Set up a Minecraft or Factorio server?

Once you have decided on what you want to do, try to do it in your virtual machine.
Once you understand how to set it up and configure it to your liking, decide on how you want to host it. I took an office computer, added a few HDDs and replaced the case with a bigger one and it’s now my home server, but any old laptop will do. Just make sure to take backups.

I used to have a Dell R710 and a virtual machine for each service I hosted, but I have moved to docker because it as simple as taking the often provided compose file, tweaking it a bit (where to store data etc) and running it with docker compose up -d.