Thread.sleep(2000);
// Store the current window handle
String winHandleBefore = driver.getWindowHandle();

// Perform the click operation that opens new window

// Switch to new window opened
for(String winHandle : driver.getWindowHandles()){
    driver.switchTo().window(winHandle);
}

// Perform the actions on new window
driver.findElement(By.xpath("ur xpath of that search box")).click();
driver.findElement(By.xpath("ur xpath of that search box")).clear();
driver.findElement(By.xpath("ur xpath of that search box")).sendKeys("ur text");


// Close the new window, if that window no more required
driver.close();

// Switch back to original browser (first window)
driver.switchTo().window(winHandleBefore);