The Shear tool should be approached with extreme caution because shearing type can turn lovingly and reverently crafted characters into a dog's dinner of distorted character shapes in a fraction of a second. That said, because the tool is there, we are bound to use it. You'll likely get the best results when it is used sparingly and applied to a small amount of type.
The Shear tool can be unruly and difficult to control: The first click establishes the point of origin for the transformation, and then you drag to make the shearing happen. It's usually easiest to make the point of origin the center point of the text frame. To maintain the proportions of your text frame, hold the Shift key.
Here's a practical example:
Figure 18.24. Sheared type.