What is Apache installed for?

Question

Apache HTTP Server

Install Nginx:

sudo apt-get install nginx
sudo service nginx start

Then, I check the work, I see an nginx page on the Localhost page, great!
Next, I want to install php, I need php 5.6, without looking for a long time I find this:

sudo add-apt-repository ppa:ondrej/php
sudo apt-get install php5.6

As a result, I install all this, the php version is necessary, but the page on localhost changes to Apache.

Question: where and why is apache installed?

Answer 1

php5.6 seems outdated to me...
apache and nginx are all web servers. Sometimes used in conjunction. apache is the main one, nginx is for the cache, for example, to speed up the issuance of pages.
If you don't need apache, install php-fpm: apt-get install php-fpm ("fastCGI process manager").
apt-get when installing php5.6 looks for dependencies and adds apache.

Answer 2

why is apache installed?

apache is a server. It can run the technology stack of your choice (for example, php, mysql, etc.)
in your example it is installed from the repository