What is a yoke?

It was suggested the Plishtim tie two cows who have not carried a yoke to the wagon....a yoke is often used to help the animals plow a field. Below are some images and videos of animals with a yoke. Can you see how a yoke would help them plow a field?

וּשְׁתֵּי פָרוֹת עָלוֹת אֲשֶׁר לֹא עָלָה עֲלֵיהֶם עֹל