To add a customizable shape:
1) Click on the Add Graphics tray below the book and then click the "Add Shape" button in the upper right corner of the tray.
2) Choose the shape you'd like to add
3) Click on your shape to choose color, frame etc or grab a corner or top /bottom/left/right side to re-size
Keywords: custom shape, rectangle, square, line, make my own shape, draw my own shape, draw a shape, draw a line, draw a rectangle, create a box, draw a box