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.
Kinda funny to depict Musk as the driver of a car, that he promised would be fully self-driving by now.