You can easily set and view due dates in Dart, both on dartboards and individual tasks.

To see dates in your board or list dartboard layouts, click on the top right dropdown menu at the top of your screen, click on the add button "+" under properties, and choose dates. Note that in calendar and roadmap layouts, dates will always be shown.

Once you have set date visibility as a default on your layout, not only will you be able to see existing dates, you'll also be able to hover over the task in the date column and have the option of adding/changing start/end dates:

To show due dates by default in individual tasks, go to:

Settings > Properties > Dates

From here, you will be able to edit how the property appears within individual tasks. You can choose to show just the due date, or a date range and/or duration. You can also choose to include dates for subtasks (if applicable).

A date, once visible, will show up in your task under your task title:

When viewing your task, you can always change your due date by hovering over the property: