The airbrushing is really really easy and gives you a nice and professional look of your backgrounds. Since i use this on my cards i never mask my images anymore. I either start like shown here or i stamp the image first and carefully brush around the image.
My card is going to be a winter card and i picked a blue for the sky that matched my patterned paper B02. Insert your Copic Sketch marker like seen in the picture into the gun. You can not use the Airbrush System with Copic Ciao makers!
Next, i start pushing the trigger all the way down and start out holding the gun fairly wide off the paper. Once i see how the color appears on my CS i hold the gun as close to the paper you see on the picture. If you do not push the trigger in a constant position you will get splatters and uneven color on your paper. (the splatters can be a nice effect too especially if you airbrush your flowers! ... i have done that before too... i buy white Prima flowers (see an example on my Sarah Kay card here) and airbrush them into the color i need them to be)
darker than others, because i know where i will add my images. I left on purpose the bottom part white, that's where my "snow" will be.
Now, i stamp with my stamp my image right onto the blue airbrushed cs
Using a dark brown color will hide completely the blue and you will not see it later on your card even if you hold the card in your hands. (at this point i added 2 shades of browns not yet blended) I lift with my Copic blender pen the blue out where the snow is on the fence.