The Blend IDE can be a strange and mysterious place for many developers. As you most likely already know, Blend, in general, is a tool to generate XAML for WPF and Silverlight applications, using a fancy graphical environment.

Similar to Visual Studio, Blend maintains a pallet of controls which can be placed on the visual designer surface, after which point they can be configured using the Properties window.

Naturally, as you are creating a UI, you may need to relocate or reposition items on the designer, and this simple task smacks you right into the odd distinction of a "Selection" and "Direct Select". If you examine the Blend Tools pallet, you will see two selection icons to represent each possibility:

Now, assume you have placed a Button control and a rendered geometry (via the Pencil tool) onto the designer.

If you wish to simple select an item for the purpose of resizing, moving or rotation, you will want to use the Select option (press the V key as a keyboard shortcut).  Once you have done so, you will be able to tweak the selected item as you see fit:

This being said, what is a "Direct Selection" used for (press the A key as a keyboard shortcut).  Well, the answer is "it depends".  If you perform a direct select on a rendered vector graphic, it will allow you to redefine the path itself using a set of pull points:

If you perform a direct select on a ContentControl derived item (such as a Button) it provides a way to drill into the internal content of the control. This can be helpful if you have (for example) a Button which set the Content property to a layout manager (a Canvas perhaps) which contains some number of sub items. In this case, a direct select will allow you to edit the internal aspects of the Button, rather than its general dimensions and placement.

Enjoy!