Resizing and Reshaping
Resizing Shapes and Groups - When in selection mode, clicking on a shape in the document will select it. Selected shapes appear with eight knobs around their edges; dragging one of these knobs will resize the shape. Note that a multiple selection acts like a group, with eight resize knobs around the selection.

Holding the Shift key will make it resize proportionally.
Holding the Option key will make it resize from the center.

Resizing Text Boxes - Text boxes are shapes that have been set to autosize when text is entered. Selected text boxes appear with two knobs; dragging one of these knobs will resize the text box horizontally. Once a text box has been resized this way, it will no longer automatically resize horizontally when text is entered. If you want to return to automatically resizing horizontally, use the Text Position inspector.

Reshaping Polygons - Click on a polygon with the selection tool to select it -- it'll appear with a blue knob at every point. Any point with a knob can be moved. Additional points can be added by double-clicking anywhere on a polygon border. Pressing Delete or Backspace with a point selected will remove it.

Reshaping Lines - A selected line will have a red knob at the tail point, a green knob at the head, and blue knobs at any intermediate points. Any point with a knob can be moved; the head and tail can be moved to connect them to or disconnect them from shapes and other graphics. Additional midpoints can be added by option-double-clicking anywhere on a selected line. Pressing Delete or Backspace with a point selected will remove it.