There are two ways to embed a Google spreadsheet:
1. Place the following code in the HTML source of the page you want the spreadsheet on replacing
http://spreadsheets.to.url
with the URL of your Google spreadsheet.
{{ google.Spreadsheet{uri: "http://spreadsheets.to.url", width: "825", height: "680"} }}
2. Use the Insert/Modify Extension from the Deki page editor shown below:

and select the Google library extension and then the google.Spreadsheet option. At this point you simply follow the prompts.