Polygon Tool

The Polygon Tool creates polygonal shapes and paths (shape outlines).

• In the Toolbox, select the Polygon Tool.
• In the Options bar, choose a drawing mode: to create vector shape layers click "Shape layers" button; to draw paths (shape outlines) click "Paths" button; to create rasterized shapes in current layer click "Fill pixels" button.
• Set number of sides in Sides field.
• Click on next to button on the Options bar to set geometry options.
• Choose shape color.
• Drag on the image.
• When creating multiple shapes, use selector on the Options bar:
  • Create new shape layer - to create every new shape in a separate layer
  • Add to shape area - to create mutiple shapes in the same vector shape layer.
  • Subtract from shape area - to subtract shapes from the current shape layer.
  • Intersect with shape area - to intersect new shapes with existing one(s) in the same layer.
  • Exclude overlapping shape areas - to create new shapes in the current shape layer subtracting overlapping areas.
• To apply some special effects to created shape layers, choose a style in Style picker (Options bar).
• When creating paths, you can select add, subtract, intersect and exclude overlapping modes.
• Working in Fill pixels mode you can also In the Options bar, choose opacity and blending mode.

Tip. Just in case you didn't know, the Polygon tool is also available in Photoshop Elements that is way cheaper version.

And if you believe, Photoshop Elements lacks some other important feature, be sure to visit this page.