This is an Autoshape tool that includes text inside the textbox. Refer to the Microsoft Word Callouts examples.
Click on Callout to activate it. (It is now dark grey.) Refer to the Figure below.
Click on the Callout to select it, place the mouse cursor on the chart, click and drag to the location. (The small squares on the sides indicate that the callout has been selected.)
To move the object to another location, click, hold down and drag it to the new location.
To resize the shape of the box, click on a corner square and drag it to the desired size.
To remove the Callout, click on the object inside the squares and press Delete to remove it from the chart. Refer to the Figures below.