(These instructions are for Linux)
To install:
sudo apt-get install apache2
To test:
http://localhost or http://127.0.0.1
To modify location of homepage:
edit (using nano or gedit) /etc/apache2/sites-enabled/000-default.conf
(edit so /var/www/html is the default directory)
To restart Apache, if you change the default directory:
sudo /etc/init.d/apache2 restart