The idea of a function is to assign a set of code, and possibly variables, known as parameters, to a single bit of text. You can think of it a lot like why you choose to write and save a program, rather than writing out the entire program every time you want to execute it.
To begin a function, the keyword ‘def’ is used to notify python of the impending function definition, which is what def stands for. From there, you type out the name you want to call your function. It is important to choose a unique name, and also one that wont conflict with any other functions you might be using. For example, you wouldn’t want to go calling your function print.
Sample code for this basics series: http://pythonprogramming.net/beginner-python-programming-tutorials/
Python 3 Programming tutorial Playlist: http://www.youtube.com/watch?v=oVp1vrfL_w4&feature=share&list=PLQVvvaa0QuDe8XSftW-RAxdo6OmaeL85M