In many project-methodologies and in projects in general it's common to estimate time and/or points to different tasks/stories. This is often used in the SCRUM-methodology, as an example each card gets a certain amount of story points, these estimations helps to gauge the timeline of a project or process. It may also influence the order of priority.
Click on your avatar in top right corner, go the App store and under Productivity you can toggle on the Card estimation field. You can name the estimate to what suits you best, in the fields you write your desired estimate in singular, plural and short.
When toggled on there will appear a field within your cards where you can set an estimation on that specific card.
After you've set an estimation on a card there will appear an icon on that card showing your estimation.
You can also choose to show summarization of estimations on boards, lanes and columns. By clicking the hamburger menu of your board and Show you can toggle it on or off.
The total sum of your estimations is shown on both the board, the columns and the lanes.