You can slap Apache on any Linux/FreeBSD/Unix type OS, or IIS on any Windows Server 2k/2k3/2k8 OS, running on standard PC hardware, and have a basic web site running in minutes. Both Apache and IIS require a bit of studying to learn how to configure, though.
If you want something really simple to configure for personal use on Windows, try Abyss Web Server.
Now, what I mean by "basic web site" is it will display static HTML pages, do some CGI scripting, and little more. CGI is a simple way for a web page to be translated into calling a program and returning it's output, this is your other option besides your web server just showing you a file on your hard drive.
More advanced web applications use a scripting/execution framework instead of CGI and need a database system which you have to install separately. On the Linux/FreeBSD/Unix side, the PHP framework and MySQL RDBMS is very popular, with PostgreSQL RDBMS also being used quite a bit. On the Windows side, you're talking about installing some version of SQL Server, and for framework choices you have ASP .NET and probably others I'm not familiar with.
Now, if you are trying to run a real web site capable of supporting thousands of concurrent users, you'll need to spread out. You wouldn't run your RDBMS on the same machine as your Web server, and you might even run multiple Web servers that are configured to load balance between themselves. This is very advanced stuff in which I don't have a lot of experience. You also want to run on real server hardware which is built to be run 24/7/365 and in which components can be switched out on the fly, so your website doesn't go down if a hard drive crashes or what not.
Web Servers need a moderate amount of RAM, but RDBMSes can take all they can get. CPU can accelerate execution frameworks but most of a Web server's work is I/O bound, meaning making network and disk faster will help more than installing a faster CPU.
It's not possible to give you a simple step by step list of instructions because there are just too many options. However, if you are looking for something real simple just to start learning, get Abyss Web Server and install it on a Windows system. It's not hard to install.