By and large, one of the most common uses for Photoshop is editing portraits. Retouching skin is a delicate art that takes a while to master, but this great video will help you get started.
This tutorial from Nathaniel Dodson will walk you through many of the basics for retouching blemishes. Like most things in Photoshop, there are many ways to accomplish the same task, with different considerations for each method and varying benefits. Dodson introduces five tools, ranging from the one-touch simplicity of the Spot Healing Brush to the fine control offered by frequency separation. Perhaps the most important consideration of the video, however, is to notice how he does the retouching on a separate layer whenever possible, making it nondestructive and allowing him to mask in and mask out changes whenever and wherever he desires. This is important as it allows you to avoid having to redo the entire process should you need to undo small changes after the fact. On a different note, frequency separation can be a powerful but overused tool, so to really dive into it, be sure to check out our Ultimate Guide to Frequency Separation, which will walk through every step, from what frequency separation is to using it to retouch a multitude of things.