After trying Apache Httpd web server to run on default port 80, e.g. on your local machine, you maybe receive an error like „could not bind to 0.0.0.0.80“.
Check if you have any other software running which could possibly use port 80. In some cases e.g. it could be Skype. If you first start Apache and then Skype, it should work. Skype then uses another port.