So one of the steps to installation is the following, and yo can see the errors:

ray@USN:~$ sudo apt-get install php5 libapache2-mod-php5 php5-mysqlnd
Reading package lists... Done
Building dependency tree
Reading state information... Done
Package libapache2-mod-php5 is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

Package php5 is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

E: Package 'php5' has no installation candidate
E: Package 'libapache2-mod-php5' has no installation candidate
E: Unable to locate package php5-mysqlnd

And here is the version of PHP I am running:

ray@USN:~$ php -version
PHP 7.0.30-0ubuntu0.16.04.1 (cli) ( NTS ) Copyright (c) 1997-2017 The PHP Group

Zend Engine v3.0.0, Copyright (c) 1998-2017 Zend Technologies
    with Zend OPcache v7.0.30-0ubuntu0.16.04.1, Copyright (c) 1999-2017, by Zend Technologies

Thanks

Ray