Hi Alessia and welcome to the forum!
Well, I can't leave you in "a blond moment", so I'll explain a little more.
Channel blending is a very powerful technique. It allows one to adjust pixels using data that's already in the file. Strictly speaking, any time you use a blend mode other than Normal or lower Opacity, you're blending channels.
Having a basic understanding of channel structure is essential to getting the most out of this technique. Take a look at
this tutorial for more information about channels.
The Channel Mixer is very useful for basic channel blending, but as I noted it's limited in that it doesn't directly allow the use of blend modes. Another limitation is you can't mix channels across color modes. One thing it does allow, however, is to blend channels at more than 100%, something Apply Image won't do.
Apply Image is my preferred tool for channel blending. If you're new to this command a detailed discussion of it can be
found here. It's one of the most powerful tools in Photoshop and one that few people use to its fullest extent. I'll post a tutorial on some of the ways I use it sometime soon, meanwhile here's the basics.
"Apply Image" works on the channel or mask that's selected at the time you open the dialog box, which is referred to as the "Target". The channel/mask that is being applied to the "Target" is called the "Source".
Here's a little test run to get you started. This example is best done with a normally lit headshot:
Duplicate the background layer.
Set this new layer's blend mode to Luminosity.
Go to Image>Apply Image.
The "Source" will be the image you're working on.
Set "Layer" to Background.
Set "Channel" to Green.
The "Target" is always the working image.
Set "Blending" to "Normal".
Set "Opacity" to 100%.
Click "OK".
You should see the contrast change without affecting the color. This is what I referred to in my last post as a luminosity blend. Most of the time this technique will make a nice improvement to the skin tones.
After reading this post and the links I provided you should have a much better understanding of what I did to your image.
Good luck and have fun,
Michael