What is the CLASS selectors used for?

Class selectors are the selectors which are stand alone to a specific style that is declared. Class attribute can be used to declare the style and make an association with any HTML element.
The syntax for creation of class selector is: .classname.
The name can be from a-z, A-z or in digits.
The example code is shown as below:
.head{font: 12em;}, this is a class selectorthis is the class that is associated with the element .