Selenium can be extended through the use of plugins. There are a number of plugins created and maintained by third parties. Google Chrome driver is one of them. Below are the steps for how to download google chrome driver:
Step 1: Navigate to Seleniumhq Download Page
Step 2: Click on "Google Chrome Driver" link in "Third Party Drivers, Bindings, and Plugins" Section
Step 3: Click on "Latest Release: ChromeDriver 2.37", There could be different latest version for you
[There is possibility that you have to repeat same step on next page]
Step 4: Click on Link "chromedriver_linux64.zip" on below page
Step 5: Extract the file and store in desired directory.