The task description is present in every tasks, and is a convienent space where you can give information on the task.

Click inside the description box, and start typing.

You can add headings, style your text, and add checklists and checkboxes by using the icons below.

The description will auto-save when you click outside of it, but you can always save it manually by clicking the save button on the bottom right of the text box or by using the cmd+s or ctrl+s keyboard shortcut.