Building creates the application's .dll and .idy files in the New_Configuration.bin subfolder of your project.
By default Eclipse builds your project automatically whenever you save a file. If you haven't configured Eclipse to do this, you can build a project at any time by selecting the project in the COBOL Explorer view and clicking Project and then Build Project to build the currently selected project, Build All to build all projects in the current workspace, or Build Working Set to build a subset of the projects in the workspace. To turn off automatic building, select Window > Preferences > General > Workspace and clear the Build automatically check box.