When viewing the details page for a work item the text fields like Description or Notes are missing and the user is unable to fill in those fields on the details page.
The missing Fields can be added back through the Show Fields option. Description is not a selectable field, but you can reset your view by deselecting another field such as Color. First deselect it, click Apply, click Show Fields again, select Color to add it back, click Apply. Your view should be reset and Description should now appear in the detail page.