Start by using the pgn4web board generator tool to create your chessboard, customizing games, colors, dimensions, bitmaps, fonts and so on. Once your desired chessboard is ready, copy the iframe URL, the URL in the yellow box as part of the src=http://... statement. Then insert a gadget on your Google sites page, selecting the Include gadget (iframe) gadget. Use the URL copied from the pgn4web board generator as the URL to content parameter and set the gadget width (suggested 100%) and height (suggested to copy the pgn4web board generator frame height value).

See example above, showing one of the most amazing opening novelties ever played in a world championship match; interestingly, the first game with the new move ended with a quick draw, only the following one rewarded Black's preparation.

Keep in mind that this method only supports relatively short PGN data (usually up to four games without comments). For larger PGN games collections, it is recommended creating a dedicated pgn4web chess page on a separate site and include that page as the URL to content parameter.