Finally, there are some general keywords related to programming/systems that you may want to look into using a reliable source (unfortunately the first page of google is filled with SEO trash, wikipedia is a better source, if you really want sources/resources I am willing 2 help but I don't have time to type much more at the current moment):
Javascript - This is the programming language showdown is written in
NodeJS - This is the program that runs the javascript to actually run showdown
VPS - you can run ur showdown server on your own computer and let other people connect to your personal machine, or you can buy a VPS. a VPS is a remote computer owned by some big software company (google, amazon, etc.) that you can manage as an admin, and the software company guarantees things like high uptime. look into good VPS services - go with a big brand with simple pricing (VPS pricing can be cheap but can also be immensely complicated and you can be hit with exorbitantly high bills out of nowhere sometimes)
Ports and port forwarding - you'll need to understand these if using either your own computer or a VPS (but VPS handle some of the oddities for you sometimes so it will be simpler to allow other users to connect if you use a vps)
Linux and the terminal - 99% of VPS will be on linux (windows is more expensive and worse for stuff like hosting servers), and almost 0% of vps will give you a nice graphical environment. you will need to use the terminal like it is 1970. two resources on the Linux terminal are
this and
this
ssh and filezilla - ssh is what you'll need on your computer to connect to your vps (if you go down the vps route) and filezilla is a good way to transfiler files and stuff onto your remote machine