I just got into self-hosting about a week ago and started by getting a small beelink s12 mini. Since you have an old pc you don't need to worry about hardware for now.

To get going with the software I followed this (https://lemmy.world/post/6542476) lemmy post in the beginning. It took me a couple of evenings to understand some basic concepts and after getting everything going I found the recommdation for https://yams.media/. So I wiped everything (because I decided to not encrypt the system and to go with Ubuntu 22.04.03 LTS instead of 23.10) and was supprised how quickly I had yams running again.

So just follow the guide and ask here or on the yams discord if you have any questions during the installation.