This page describes how to get Apache and php running on a computer running Debian 9 (nicknamed Stretch). These installation steps will probably also work on kindred systems like Ubuntu and Linux Mint. In case it doesn't work out for your Linux system, search the web for help on installing a so called 'LAMP' stack (for Linux-Apache-MySQL-Php), there are lots of tutorials to be found.
1. Install Apache and php
Open a terminal and type
sudo apt-get update
to update the repositories, then
sudo apt-get install apache2 php libapache2-mod-php
If you now open a browser and navigate to 'localhost' you should see a page with the reassuring text 'It works!'
2. Enable url rewriting
Still in terminal, enter
sudo a2enmod rewrite
to load the rewriting module, then restart Apache with
sudo /etc/init.d/apache2 restart
3. Set up a webfolder
Create a folder where you want to place your website(s), e.g. /home/username/www
In terminal, type
sudo nano /etc/apache2/sites-available/000-default.conf
This opens a text editor. Change the line
DocumentRoot /var/www
into
DocumentRoot /home/username/www
Close and save by pressing CTRL-X and then Y.
4. Test
Create a file in your webfolder, named 'index.php' with the following content
<?php
echo 'Hello world';
?>
And use your webbrowser to navigate to the address 'localhost'.