Build a project
When you are ready to build your project into a working application, you can use Build Project to build it. Building also makes new user controls, custom controls that are defined in class files, and controls that are defined in .dll files available from the Asset Panel.
Building is not necessary for Microsoft Silverlight 1.0 projects. For more information, see Test a Silverlight project from Expression Blend.
Make sure that you have the correct project open in Expression Blend, and then, on the Project menu, click Build Solution. You can also use the commands Rebuild Solution and Clean Solution on the Project menu as part of your testing and build efforts. Rebuild Solution rebuilds everything, including components that are built from files that have not been changed. Clean Solution deletes all intermediate files that are generated by the build, but will not rebuild the project.
In the Results panel, review the build process for any errors that may have been returned. If you encounter an error, the build will be unsuccessful, and you will have to repair the error before you can successfully build the project.