What is the function of a data type?

A data type is the principal of a computer programming language. It has predefined characteristics. In other words, it defines the instructions and functions/values in code. So for example: In a computer language, a term such as a Boolean gives the action of being either true or false. It is only that because it is predefined. Sorry, if you don't understand that but if you are asking a programming related question, I assume that you have an idea already ...