Build a project
When you are ready to build your project into a working application, you can use the Build Project command to build it. Building your project also makes new user controls, custom controls that are defined in class files, and controls that are defined in .dll files available from the Assets panel.
Make sure that you have the correct project open in Expression Blend, and then, on the Project menu, click Build Project. You can also use the commands Rebuild Project and Clean Project on the Project menu as part of your testing and build efforts. Rebuild Project rebuilds everything, including components that are built from files that have not been changed. Clean Project 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.