Project configurations are used to create different software builds for your projects. A configuration is used to define different project property values, for example the output directory of a compilation can be put into different directories which are dependent upon the configuration. By default when you create a solution you'll get some default project configurations created. 

To select configurations

You can set the configuration that you are building and debugging with using the combo box of the Build toolbar or the Build | Set Active Build Configuration menu option.

To create configurations

You can create your own configurations using Build | Build Configurations which will show the Configurations dialog. The New button will produce a dialog that allows you name your configuration. You can now specify which existing configurations your new configuration will inherit values from.

To delete configurations

You can delete a configuration by selecting it and pressing the Remove button. Note that this operation can't be undone or cancelled so beware.

Hidden configurations

There are some configurations that are defined purely for inheriting and as such shouldn't appear in the build combo box. When you select a configuration in the configuration dialog you can specify if you want that configuration to be hidden.