Labels are usually used to display some text information on the plot.
A label is characterized by its caption, size and color, position. It may have vertical and horizontal lines (this is usually used to point to the function's vertical or horizontal asymptotes). A label can be dragged easily using a mouse. However there is need sometimes to disable this ability for a particular label to avoid occasional movements. A label can be locked (see the Label dialog box for this option). When you lock a label then its focus is drawn with empty rectangles while they are filled when it is unlocked.
Click the Graphics|New|Label main menu command to create this kind of graphics. This will cause the Label dialog box show where you can modify it's properties.
Label Dialog box
The Caption box prompts you to enter the label's caption (the text that will be displayed on the plot at a specified position).
Visible option allows you to temporarily hide a label without deleting it from the project.
The Locked option locks a label, so you will not be able to drag&drop it using a mouse.
The x and y boxes entries must be any mathematical expressions including constants. These are the coordinates of a label. Find those controls on the Location tab.
Select Horizontal and Vertical boxes form the Lines tab to add horizontal and vertical lines to a label.