Working with Photoshop is a continual learning process. There are so many tools and manipulations to learn, I think I could continue for the rest of my life and still not learn everything. I have taken some incredible classes and watched some great tutorials from fantastic photographers like Barb Uil of Jinky Art and Meg Bitton.
I am not here to give you advanced information that I have learned from them. If you are at that point I encourage you to sign up for Barb's Video Tutorials or one of Meg's Webinars.
If you are just starting out then I am the girl for you. I am here to help you learn the basics of photoshop in an easy to understand, straightforward way.
The pen tool is something I just started working with this year, and mostly with my architectural photographs, but I can see how its precision in selecting areas could be helpful with portrait images as well. If you are working on an image with an angular selection that you need to be exacting with, this is the tool to use!