How does “do something OR DIE()” work in PHP?

Question

I\'m writing a php app to access a MySQL database, and on a tutorial, it says something of the form

mysql_connect($host, $user, $pass) or die(\"could not con         


        

Answer 1

$con=mysql_connect($host, $user, $pass)
if(!$con)
{
     die("could not connect");
}
else
{
     echo "Connected";
}