There are other videos out there discussing frequency separation, and how to use it for models and headshots. This one is easily the best, since it goes into detail about what you’re doing and why.
If you didn’t know, frequency separation is the method in Photoshop to do a real, but tasteful retouching. If you look at a model’s picture and you think “this looks airbrushed,” then they didn’t do it right.
By carefully minding how you “airbrush” a model’s images, you can clean up blemishes and color irregularities, while keeping the humanity — and appearance of reality — in the picture. In simple terms, what you do is to smooth out tones in the face, while keeping the pores intact. This doesn’t happen if you’re using the clone tool a lot, or if you’re doing some gaussian blurs. Blurring effects on skin tone can be a bit like throwing the baby out with the bathwater. While it will smooth things, it will also kill some of the finer detail that you want to keep, that little detail without which your model is thrust into the uncanny valley; that is, looking a little bit un-human.
Anyway, if you’re a beginner or an amateur, or even intermediate in photo retouching, you may not know about this method for professional image editing. It’s very much worth learning about.