Visual Studio uses the Configuration Manager to determine which projects in a solution are automatically included in a given build or deployment configuration.
Some templates that are generated with a referenced library project will already have the referenced library included in the configuration; but otherwise it will need to be set manually.
How to use the Configuration Manager
- Open "Build -> Configuration Manager"
- Select the configuration to customize, e.g. Debug | iPhone
- Select checkboxes for the projects you wish to include. Note: Greyed out boxes are handled automatically, and shouldn't need any changes.
Screencast of these steps: http://screencast.com/t/zLoQOpEn