Start the webserver
sudo launchctl load -w /System/Library/LaunchDaemons/org.apache.httpd.plist
If you want to restart it:
sudo launchctl stop -w /System/Library/LaunchDaemons/org.apache.httpd.plist
sudo launchctl start -w /System/Library/LaunchDaemons/org.apache.httpd.plist
Documents are in:
/Library/WebServer/Documents
Configuration is in:
/etc/apache2/httpd.conf