Highlighting, or selecting, text will allow the user to perform certain actions on the selected text, which include copying, deleting, bolding, underlining, and assigning color. Once the text is highlighted, the action you perform will affect only the highlighted text.
To highlight text, place your cursor to the right (or left) of the text to be highlighted, press and hold the left mouse button and move the mouse over the text. When the desired text has been highlighted, release the mouse button.