A callout is a text note within a shape such as a rectangle with one side pointing at an object. A simple method for creating a callout is explained below.
Use the quickshape tool to make a rectangle (with rounded corners if desired)
Right click on the rectangle and Convert To Editable Shapes
Click on the Shape Editor Tool and add three points where you want the triangular part to be
Drag the center point (of the three you just added) toward the object the callout points to.