The Apache HTTP Server Project is an effort to develop and maintain an open-source HTTP server for modern operating systems including UNIX and Windows NT. The goal of this project is to provide a secure, efficient and extensible server that provides HTTP services in sync with the current HTTP standards.
Apache has been the most popular web server on the Internet since April 1996.
The Apache HTTP Server is a project of the Apache Software Foundation.
http://httpd.apache.org/
Download and install Apache from http://httpd.apache.org/download.cgi.
Look for the Win32 Binary version.
When you install Apache, you'll get a prompt for Server Information. Here are the settings I've used:

I recommend you to check for All Users, on Port 80, as a Service.
If you choose Typical setup and C:\apache as your installation folder,
it'll actually be installed to C:\apache\Apache2.
In Custom setup you can specifically choose where to install each of it's parts/sub-parts.
After installing, Apache2 will automatically start.
start icon in the system tray means it is running.
stop icon means that the Apache server monitor is running, but Apache itself hasn't started.
You can easily start | stop | restart Apache via that icon in your system tray.
If you get the error The requested operation has failed! while starting apache try the Test Configuration shortcut in the Start Menu to find the error (if the console window pops up and closes before you can read it, it means that your configuration is fine).
Now the ultimate test to see if it's all working.
Open your browser and head to http://127.0.0.1/ or http://localhost/.

If you see the above Apache installation's test page then you have your server configured and running.
C:\<APACHE_INSTALLATION_FOLDER>\conf\httpd.conf
and search for DocumentRoot.
DocumentRoot C:/<APACHE_INSTALLATION_FOLDER>/htdocs to the
location where you will place your HTML files (e.g. DocumentRoot C:/public_html).
<Directory "C:/<APACHE_INSTALLATION_FOLDER>/htdocs"> to point to the same location
you set DocumentRoot to in the last step.