Web server and operating system information

What is a web server and which is the best?
Web Servers List
What is Apache and should it be a part of my web hosting?
On which operating system (or, platform, in tech jargon) should I host my web site?
Unix, Linux and FreeBSD operating systems for web hosting servers
Windows operating systems for web hosting servers
How is a web hosting Server different from your home/office machine?
I am not happy with my present web hosting. Can I change it?
How do I change my web hosting server?