Go to the google gadgets site(http://www.google.com/ig/directory?synd=open) and find the one you want and click on the title.

Then just click the add to your webpage button.

Adjust the available settings to your likings and click the “Get the code” button. Copy the code it generates to the clipboard.

Now go to your SharePoint site and add new content editor web part the page you want the gadget on.

Click the web part menu (little triangle in the top right) of the content editor web part and go to Modify shared web part.

In the tool pane click the source editor button and then paste the contents of your clipboard in the window that appears. Click Save on the pop and then OK on the tool pane.