I don’t mind if you link me to some youtube channel or some website that explains this as long as it’s just a simple network and nothing harder.

I’ve got to rush right now but starting with :
“first have a couple of PCs connected to a server”

I’d back up and start with :
What’s the nature of the ‘network’ ? Is it ethernet wires? Is it WiFi ? Are there hubs and switches and routers ?
Then how are each of the machines connected to the ‘network’ ?

Then get into what resources are on the network, like a server.
What does the server do for the rest of the machine? E.g. file service ? An http server ? A database server ?

etc.

Uh, I’d do this really incrementally. I’m assuming you mean Windows PCs. PCs don’t necessarily run Windows and, much as Justin Long likes to pretend otherwise, Macs are basically PCs too. It might help if you tell us what equipment you have and what your basic level of knowledge about computers is, and even what you want to do – because even ideas like a “shared drive” are a little vague, as there are lots of ways to share your drive.

I think the basic information you want/need follows:

First, the network: a simple home network can consist of a bunch of machines plugged into a switch. The outbound port can optionally be connected to the Internet through a NAT router – in fact, that’s what most home networks are and this is as far as people go. You probably have something like this already, or have at least seen it.* The most likely basic configuration for such a setup involves a DHCP server assigning network addresses on your LAN on a fist-come-first-serve basis. This should be sufficient for a basic network with Windows-style filesharing.

Next, filesharing is modestly more difficult. You need to pick one machine and designate it as a “server.” It can be any machine working on the network above. It’s nothing fancy. A simple Windows-based filesharing system can be achieved by setting a common “Workgroup” and then sharing a folder in Windows Explorer (Hold the Windows Key+R, type ‘Explorer’, and hit Enter; Explorer pops up and you can right click on a folder go to Sharing to set it up). A major caveat here is you probably need to tweak or disable your firewall.

Better filesharing and authentication: you have a lot of options here, but they tend to be complex. The easy way might to be to drop a lot of money on some version of Windows that does what you need, but that’s expensive. The “cheap” (financially) way is to get some species of Linux or BSD and run samba for file sharing and authentication alike. A basic samba network is relatively easy to set up, but it can get very complex too.

* The caveat is, in most cases the router and the switch are one piece of equipment. You can add another switch if you need to connect more machines. A switch looks like this. There are other slight variations on the same idea for home network users. Sometimes a single device is a switch, router, and cable modem, but that shouldn’t matter.

† MacOS X is a bastardized version of BSD, and counts here, though I would advise against spending money on a Mac if you don’t already have one

@bolwerk What you said.
Although I’d add the option of the peer-to-peer mesh sharing paradigm as an alternative to the server paradigm, for ad hoc events and sharing configurations.