Selenium Virtual User (VU) scripts are written using the Java programming language, and use Selenium WebDriver to automate web browsers. Selenium WebDriver provides an object-oriented API that provides a common interface for driving all of the major browsers (Internet Explorer, Firefox, Chrome, IPhone, etc.). It can also drive the HtmlUnit GUI-less browser, which is the fastest and most lightweight implementation of WebDriver, and hence is the most appropriate choice for a load testing application.
Each Selenium VU represents a single WebDriver instance. This instance can be accessed in your scripts by calling the getWebDriver() method:
WebElement logInLink = getWebDriver().findElement(By.linkText("Log in"));
This code gets theVU's WebDriver instance, and then uses the findElement method to find the Log in link on the current page.