How do I make my home computer to become a web server?

For starters, download apache...

http://httpd.apache.org/

It all depends on your operating system. If you have win 98 you can install "Personal Web Server", it is on the win 98 CD in the goodies folder (if I am not mistaken) or add it on the components section in your "add/remove programs". If you have win 2000 you can do the same.

Or you can go out on a limb and install apache. All depends on your needs and skill level.