The 'Display Fields' screen is where you can control when field values and labels will appear in your content. Each field is listed on the screen, and you can select whether the label should be hidden or appear above or next to the field value.

For each field, you can choose how the field will be displayed in the teaser and the full node view by selecting the 'formatter' to use in that view. The exact formatters available differ depending on the type of field you are using. For the 'Text' field, you have a choice of 'Default', 'Plain text', 'Trimmed', or 'Hidden'. 'Default' will display the normal view of the text, as HTML if html is used, and filtered with the selected filter. 'Plain text' will display the raw text from the field with no HTML. 'Trimmed' will trim long textareas down to the length selected for post teasers, and 'Hidden' will not display the field at all. So you could choose to hide this field in the teaser, but display it in the full view.