When creating an MVT or multivariate test, you create several variations for different elements within a webpage. Assuming that you have a webpage that

Headline: my headline

Image: happy family

Call to Action button: Red button

In an MVT test, you can provide several variables for each of the elements (headline, image, call to action)

Headline: my headline or my headline or headline 3

Image: happy family or woman

Call to Action button: Red button or green button or blue button

The number of test designs depends on the number of elements and the number of variables for each of the elements. When a visitor lands on the webpage, the testing software will choose one of the values for each of the elements and serve it to the visitor. When the test concludes, you choose the winning design (the one which is converting more or generating more revenue) and implement it permanently on your website.