Users who are signed in and viewing a story have the ability to up vote / like or down vote / dislike items by clicking the thumbs up or thumbs down icon when the item is open as shown below.

Once an item has one or more votes, mousing over the total will show the users who cast the votes. 

This item property can be used in calculations, as well as for plotting your items on a 3D, Timeline,  Compare, List, or Grid view. Simply select Like Count or Dislike Count from the Properties list in your View Setup window as shown below. 

In the example below, you can see that the Technology Refresh item has 1 vote while the other programs listed have 0.