Variations and Factors work together. A Factor is the content that you want to modify on an existing web page during a Campaign. A Variation describes how you want to change the Factor. If the Factor is a button, the Variation may change the color of that button. If the Factor is a line of text, the Variation may change the content of the text.
For example, if you want to test the effects of enlarging your Checkout button and moving it to a different place on the web page, create two Factors: one Factor for the button size and one Factor for the button location on the page. Then create Variations of each Factor, i.e., variations in size and variations in position. To test these Factors at the same time, add them to the same Campaign. This creates a multivariate test using these button variations.