In Google Sites, all edits that you have saved will be automatically logged and recorded. Only page edits are recorded in history; comments and attachments are not recorded. You can access the page history by going to the page you want to view, clicking on the More Actions button at the top right and selecting Revision History from the menu.
The page will now display all edits made to the page since it was created as well as the name of the person editing the page and the date it was last changed. You can click in to an individual version to view what the page looks like when it was edited at that time. To revert back to a previous version, click on the Revert to this version link. This will remove all edits made after that revision.
When viewing a revision for the page, you can also compare the revision you are viewing to another revision. To do this, click on the Compare two versions button. Select the other revision you want to compare the current revision to.
The page will display the differences between the two page revision. Text that has been removed will be crossed out. Text that has been added will be underlines. Text that has not been changed will contain no special formatting.