You can start the A/B test by checking the A / B test box next to the headline field in the editor.
You can then enter two different headlines. When you publish the article, the system will show headline A to 50% of the visitors and headline B to 50% of the visitors in the first minutes after publishing the article.
The headline that receives the most clicks "wins" the A / B test and will be shown to all other visitors. You can see the results of all A / B tests that you have performed here.