You need to install the following to use Vaadin Designer:
Eclipse for Java EE developers
Vaadin Designer from link: https://vaadin.com/eclipse
If you already have Vaadin Designer installed, it will be upgraded to the newest Vaadin Designer.
Choose Help > Install New Software…
Type https://vaadin.com/eclipse into the Work with field and hit Enter
On Vaadin, select Vaadin Designer.
Follow the wizard to finish installing the plugin
Restart Eclipse to make the plugin active