What is the difference between driver.getWindowHandle() and driver.getWindowHandles() in Selenium WebDriver? code example

Example: difference between driver.getwindowhandle() and driver.getwindowhandles()

driver.getWindowHandle() – It returns a handle (String) of the current 
page (a unique identifier)
driver.getWindowHandles() – It returns a set of handles (Set<String>) 
of the all the pages available