graphicxtras.com > Using Photoshop custom shapes as a source for selections and masks (via paths etc) etc tutorial
They can be used as a great source for selections. You don't need to just draw out a selection or use the rectangular marquee tool to select a part of an image. You can use the shapes to create a selection to copy and paste or fill areas with effects or add hue adjustments. You can use the same approach in CC CS6 CS5 etc. Below you can see the 'marching ants' of a selection generated via one of the flower custom shapes available on this site (though you can use any of the supplied CSH presets as well as any other third party presets)
Apply the shape in quick mask mode to create a quick selection. Quick mask mode can be entered via the toolbox. You can see it at the bottom of the toolbox just above the screen mode setting. Once you have entered the quick mask mode, you can add a shape using the pixel mode. Add the selection in black (it will be displayed in red in the quick mask mode) as well as other colors (other than white). You can also use white and other colors to remove from the black (quick mode). On exit from quick mask mode, you may prefer to invert the selection as the selection selects the entire document and not the actual path.
Go to the channels panel and menu and create a new channel via the right side menu. Select the alpha channel and make visible (eye sign) and select that channel and apply the CSH artwork (set the color to white etc as required and set to pixels option). The generated results in the channel will be in grayscale. Select menu and load selection alpha channel and you will see the selection. The artworks can be applied multiple times to create far more complex selections.
The text above has an alpha channel added and then the CSH presets are added to the work in a variety of positions across the image. The load selection (select menu) is used to load the alpha channel and the area is then filled with a solid color at 50% opacity below. A selection of flowers cover the text.
Go to the CSH tool and set to path option (can be found along the top bar) where it say 'select pick mode' when you hover over the control. Apply the path and goto the paths panel and right menu and make selection command for the currently selected work path. The path options means you can create even more amazing selections by using the direct selection tool to manipulate the path points as well as anchor points of the generated path. You can also use the pen tool to remove points from the generated path. The path below has been added and the points of the path have been distorted by dragging the anchor points away from the original design. The selection was then created and the exterior area was filled with additional brown fills leaving the path untouched. The path (with the selection) had a stroke added via the edit menu 'stroke' command. The same can be done with the layer as well if you have the path panel displayed as you can just click the 'load path as a selection' button (bottom of panel) if the path is selected in the panel.
You can also simply create a new layer and then add the CSH presets / artwork to that layer (you can add one or multiple artworks) and then use the select menu and load selection command and select the channel 'layer 1 transparency' for the selection. Below, a new layer was created and the color of the preset was set to black and then applied three times across the document and then the channel was selected via the load selection command. The area was then filled with different rectangles of solid color.
A video showing a number of ways to create selections using CSH Presets [Youtube]