Variables let you write commands that include numbers, words and other values that will be different every time your program runs. Any time your code refers to the same value (number, word, etc) in more than one place, you should use a variable.
This code creates a variable called animal, assigns it the value 'dog', and uses it to stamp a dog 500 pixels wide:
This code creates a variable called distance, assigns it the value 20, and uses it to move a car object 20 pixels to the right:
This code creates a variable called greeting, assigns it the value 'hello there', and uses it to write a message on the screen: