Today we are going to add some clouds to this photo.
To begin with, add a photo with clouds above the background layer.
Go to the channel layer, press "Ctrl" and left click the red channel.
You will find that most of the clouds are selected.
Go to the layer channel, click "add layer mask". (the one highlighted)
You will see something like this.
Use the brush tool to eliminate the clouds "in the river" and those covering the mountains.
