First, you need a use-case. It’s worthless to have a server just for the sake of it.

For example, you may want to replace google photos by a local save of your photos.

Or you may want to share your movies accross the home network. Or be able to access important documents from any device at home, without hosting them on any kind of cloud storage

Or run a bunch of automation at home.

TL;DR choose a service you use and would like to replace by something more private.