Open your 1&1 site editor, click Insert Element from the sidebar menu, and select Widget/HTML.
Copy and paste this code into the text box. Then click Save and close the Settings window.
Your plugin will not appear yet. Click the Desktop icon to view your site preview. You should now see POWr Vimeo Gallery.
You can keep editing POWr Vimeo Gallery in your site preview, or on the live page. Just click the Settings Icon to open the POWr Editor.
You can also edit this plugin any time in your POWr account dashboard.