Not able to open firefox latest browser by selenium 3.obeta2

I am getting below error, I tried to download the gecko driver but not sure how to use it. Currently I am on module 11 just on introduction to webdriver .

Exception in thread "main" java.lang.IllegalStateException: The path to the driver executable must be set by the webdriver.gecko.driver system property; for more information, see https://github.com/mozilla/geckodriver. The latest version can be downloaded from https://github.com/mozilla/geckodriver/releases
at com.google.common.base.Preconditions.checkState(Preconditions.java:199)
at org.openqa.selenium.remote.service.DriverService.findExecutable(DriverService.java:109)
at org.openqa.selenium.firefox.GeckoDriverService.access$100(GeckoDriverService.java:38)
at org.openqa.selenium.firefox.GeckoDriverService$Builder.findDefaultExecutable(GeckoDriverService.java:91)
at org.openqa.selenium.remote.service.DriverService$Builder.build(DriverService.java:296)
at org.openqa.selenium.firefox.FirefoxDriver.createCommandExecutor(FirefoxDriver.java:245)
at org.openqa.selenium.firefox.FirefoxDriver.<init>(FirefoxDriver.java:220)
at org.openqa.selenium.firefox.FirefoxDriver.<init>(FirefoxDriver.java:215)
at org.openqa.selenium.firefox.FirefoxDriver.<init>(FirefoxDriver.java:211)
at org.openqa.selenium.firefox.FirefoxDriver.<init>(FirefoxDriver.java:124)
at Drivers.main(Drivers.java:6)