how can I do anything with it?? [Edited for clarity]

Use PHP 7+ and MySQLi (improved) which replaced outdated PHP 5 and MySQL code.

As an example, add this code to a new empty document and save as test.php. 

Upload test.php to your remote server and run the code by typing its URL into your browser's address bar.

Change your_username, your_password and database_name as required.

<?php
$con = mysqli_connect("localhost","your_username","your_password","database_name");

// Check connection
if (mysqli_connect_errno())
  {
  echo "Failed to connect to MySQL: " . mysqli_connect_error();
		}
		else echo "Successfully connected, happy coding!"
?> 

<?php phpinfo() ?>

Im afraid l cannot endorse the use of Dreamweaver these days if you want to create a dynamic website which is database driven as its way behind the curve in every respect, unless you are a coder.

Many of us around here, who have been helping out in the forum for years are sick to the back teeth with Adobes broken promises to reinstate a brand new set of server behaviours to help those who do not have the necessary coding skills which will make Dreamweaver a worthwhile purchase. Currently for anything other than producing static responsive, simple websites, its useless unless you are a coder in which case you probably would not use Dreamweaver as your first choice of editor.

These may be harsh words but the whole Dreamweaver management/team/ceo at Adobe need a good  kick up the backside or at least out the real truth as to why the product has slipped so far behind just about every other web editor available, free or paid for.

Looks like you are using an older version of DW.  Those functions are out of date and it's possible your server/hosting company may not support them.  Personally speaking, as old as those functions are I would not recommend using them at all.  However, if you still want to use them, you will need to contact your server administrator/hosting provider to have them enable the functions you are trying to use.