windows tabs

Selenium can only focus on one thing at a time. 
Selenium creates something called window handle for each tab or window.
For selenium, there is no difference between 
a tab, and a window. It treats both as the same thing.
 What is a window handle: Randomly generated string 
 that is unique to each window
How to get current window handle? 
driver.getWindowHandle() will return current 
window handle as a string
How to get all of the window handles of the 
currently opened tabs/windows?
driver.getWindowHandles()  
will return a set of strings that contains all the window handles.
How do we switch to another window using its handle? 
driver.switchTo().window(handleOfTabWeWantToSwitch);
We need to create a loop to switch to windows that is 
opening later on. To switch back to the main window (default window):
driver.switchTo().window(mainHandle);