Green horn

Hi the name is Timothy.
I’ve read about and understand the basic consepts of a network.I was planning on starting one up but i have 1 problem.The availibity of a second hand or cheap server to start with.I had thought of startin from scratch.I meanwith a tower casing
but the problem is how do i really go about this
what mother board would you recommend and OS to start with.

I’ve checked trough some of the answers and seen the replies you guys have given and i know you will be able to help me too 🙂
Thank you