I want to use Selenium on Python but I have an alert message: 

driver-webdriver.Chrome("D:\Selenium\Chrome\chromedriver.exe") NameError: name 'driver' is not defined 

I have installed the Chrome Driver, what else must I do ?
chromedriver.exe must be in python path, probably now python expects that driver exists in "D:\Selenium\Chrome\chromedriver.exe" but it does not. You could try add chromedriver.exe path to windows enviroment path variable, or add path to os.path in python, or add driver to folder of python script.
"Driver is not defined" Python/Selenium