Log in at http://www.web.de with your web access data and click on Domains (A) to open the WebBaukasten (B) and then the editor.
Open Pages (A) and select the page (B) that shall contain bookingkit data. Then click on Open page (C). You will be redirected to the corresponding page.
Click Modules (A) in the editor and then drag and drop Script (B) into the page-specific area (in the preview).
At this point, a text field opens which you can insert the 2-line code for your bookingkit into.
You find this code directly in your bookingkit account under Sell -> My Widgets.
Finally, click on Publish to integrate your bookingkit widget into your website. Please note that bookingkit is not displayed in the preview, but is nevertheless added to your website.