The opacity refers to the amount of transparency of a layer. So, if the opacity is at 100% the layer is completely opaque. Whereas if the opacity is at 0% the layer will be transparent, which will mean you can see the layer below.


How do you change the opacity?

Changing the opacity of a layer simply involves moving the slider shown in the example below. To increase the opacity you move the slider to the right. And to decrease the opacity you move the slider to the left.




Opacity example

The image below is at the opacity of 100% which is the default value.



The image below is at the opacity of 50%, as you can see the image look transparent.