Almost forgot..
In my link I don't actually explain braces but basically what they do is to tell PHP to treat that variable independently to the rest of the string. This is useful if you're using an array in a string (especially multidimensional arrays) or a string which contains a character such as _ which would be seen as part of the variable if you didn't seperate them.
PHP Code:
//Example 1
$Array['chaser'] = 'dog';
$Array['neighbours']['pet'] = 'cat';//Multidimensional array
Print "The {$Array['chaser']} chased the {$Array['neighbours']['pet']}";// The dog chased the cat
//Example 2
$Array[1] = 'under';
$Array[2] = 'score';
Print "This is how you might demonstrate using an {$Array[1]}_{$Array[2]}";
//This is how you might demonstrate using an under_score
As you can see, php will treat those in braces inside a string as if they are seperate. Had I not used braces in the second example either side of the _ then PHP wouldn't have worked its magic there.