Clear All Cookie Data: You can tap this setting, and then in the Clear dialog box that appears, tap OK to clear all cookies from your device.
Clear Cache: Any computing device holds information in its cache to help it redisplay a page you’ve visited recently, for example. To clear out that cache, which can also free up some memory on your Kindle Fire HD, tap OK.
Clear History: Your Silk browser retains a history of your browsing activity to make it easy for you to revisit a site. However, it’s possible for others who view your browsing history to draw conclusions about your online habits. To clear your history, tap OK in this setting.