python - control the browser with selenium module - selenium

Question

I installed python version 3.5.2, selenium version 3.0.1 and firefox version 49.0.2.
After all of that and in my shell scripting I typed
>>> from selenium import webdriver
>>> browser = webdriver.Firefox()
and got error as this below:
Could someone guide me on what is wrong here.
I appreciate it. I am just starting out on python. Thanks
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Traceback (most recent call last):
File "C:\Users\D\AppData\Local\Programs\Python\Python35-32\lib\site-packages\selenium\webdriver\common\service.py", line 64, in start
stdout=self.log_file, stderr=self.log_file)
File "C:\Users\D\AppData\Local\Programs\Python\Python35-32\lib\subprocess.py", line 947, in __init__
restore_signals, start_new_session)
File "C:\Users\D\AppData\Local\Programs\Python\Python35-32\lib\subprocess.py", line 1224, in _execute_child
startupinfo)
FileNotFoundError: [WinError 2] The system cannot find the file specified
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "<pyshell#1>", line 1, in <module>
browser = webdriver.Firefox()
File "C:\Users\D\AppData\Local\Programs\Python\Python35-32\lib\site-packages\selenium\webdriver\firefox\webdriver.py", line 135, in __init__
self.service.start()
File "C:\Users\D\AppData\Local\Programs\Python\Python35-32\lib\site-packages\selenium\webdriver\common\service.py", line 71, in start
os.path.basename(self.path), self.start_error_message)
selenium.common.exceptions.WebDriverException: Message: 'geckodriver' executable needs to be in PATH.
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