To remove text, first select it (see Selecting text) and then right-click and select Cut (or click on the Cut button on the toolbar). The text will disappear from the document. The text is now in the clipboard, so is available for pasting if you want to do so, but since you do not have to paste it anywhere it has effectively been deleted.
Alternatively, select the text and then:
overtype with something else
press the del key or select Delete from the Edit menu
press the ¬ (backspace) key
See also: