JAYPHEN SIMPSON, PETAPIXEL:
Mastery of the pen tool enables complex vector shapes and selections that can be used for masking or extracting elements from an image. There is a bit of a learning curve to the tool, but this 30-minute video from Unmesh Dinda of PiXimperfect will teach you everything from the fundamentals to real-world use.
To fully grasp how the tool works and why it is useful, you need to understand the difference between vector and raster shapes and how the former is constructed. Dinda starts his video by explaining this with visual examples and follows up by showing how the tool can be used to construct a series of gradually more complex shapes.
Check it out, from here.