How do these Asic mining shares work? Ive seen lots of auctions for selling "shares" but I'm lost on how the work. Could anyone point me to some reading material or explain them to me?

Hello everyone, this is my first post as I am new to the game. For those that would like to build our own miners with chips and pcbs, what kind of resources are out there to support us? I'm looking for any guides and tutorials pertaining to assembly as well as purchasing parts.