The basic concept of class in php and make object of class

Basic class definitions begin with the keyword class, followed by a class name, followed by a pair of curly braces which enclose the definitions of the properties and methods belonging to the class.

The class name can be any valid label which is a not a PHP 

reserved word.  

A valid class name starts with a letter or underscore, followed by any number of letters, numbers, or underscores. As a regular expression, it would be expressed thus: [a-zA-Z_\x7f-\xff][a-zA-Z0-9_\x7f-\xff]*.

A class may contain its own constants, variables (called "properties"), and functions (called "methods"). 

the simple example of php class is following.

<?phpclass _DemoCLass{
    // property declaration
    public $Member1 = 'Value of Member1';

    // method declaration
    public function DisplayValue() 

    {
        echo $this->var;
    }
}?>

Note:-

The variable name and class name are case sensitive so when you make object of class that time use in proper way else it's give an error.

The pseudo-variable $this is available when a method is called from within an object context. $this is a reference to the calling object (usually the object to which the method belongs, but possibly another object, if the method is called statically from the context of a secondary object).

Make object of class.

//it's create a new object of _DemoCLass class

$NewObj = new _DemoCLass;

 //call method or function of class

$NewObj -> DisplayValue();

for more info visit following link,
http://php.net/manual/en/language.oop5.basic.php