To add a mask to a layer, click on the “Add Layer Mask” icon in the Layers panel. Click once to add a layer mask and click again to add a vector mask (or you can Command -click (Mac) | Control -click (Win) the mask icon to add a vector mask).
To add a layer mask that automatically hides the content of the layer (or the selection), as opposed to revealing it as it does by default, Option -click (Mac) | Alt -click (Win) the icon.
Use Command + I (Mac ) | Control + I (Win) to invert a layer mask, or click the Invert button on the Properties panel!
In this episode of The Complete Picture, Julieanne demonstrates five of her favorite new and improved features for working with vectors. Discover path creation improvements, isolation mode, drag-selecting paths, path operation shortcuts, and more.
Note: If you are new to Photoshop or skipped version 6, you might want to take a look at the re-engineered shape tools in this video “What’s New in Adobe Photoshop CS6” (vector layers begin at @ 44:45).
And, you can learn about rounded rectangles and Live Shape Properties in this video: “Adobe Photoshop: Favorite Features for Photographers”.