Opacity and Blending Modes
Transparency can be applied to objects or artwork to allow other objects to show through them. Any artwork or objects can be made transparent, as can gradients, patterns, and placed images. Open the Transparency panel under Window > Transparency to set the opacity and blending mode of objects and create opacity masks. You can also check the Knockout Group option to knock out sections of one object with a section of an overlapping transparent object. The Transparency panel does not show all the options by default; choose Show Options from the dropdown menu to display all the options.
When creating ...