In order to use your workbench extension created from the microej-extension skeleton, you need to add it to your platform. To do so, you can either declare it as a dependency in the module.ivy file of your -integration project, or add the jar file in the dropins folder of your configuration project, and then rebuild your platform.
Then, to test that the extension is working properly, import your newly created platform (or restart the SDK if it was already imported), go to Run configurations to select your launcher, make sure to select the right platform in the Execution tab and finally go to the Configuration tab. There, you should find the pages provided by your extension.