Illustrator clipping masks are used for two main reasons: to clip away parts of an imported image, and to tidy up your Illustrator artwork, for example a border with rounded corners. In our Illustrator courses we show you practical examples of both methods.
In the first example, go File > Place > and browse to the photograph or vector image you wish to “cut out”. Then use the Pen tool to draw around the shape – this can be as accurate or as rough as you wish. Modify the anchor points with the Direct Selection tool and the Add/Delete/Convert Anchor Point tools.
Then select both image and clipping mask/path with the Selection tool, and right-click > Make Clipping Mask – the image is cut out.
If you are not happy with the result, you can always go right-click > Release Clipping Mask.
The second example would be to create a Rounded Rectangle over your artwork and create a clipping mask using the same method.
See many examples of our clients’ work on our Facebook site.
Other related Illustrator Blog Posts:

• Illustrator workspace
  
• Illustrator basics