Here as you can see that the textbox for password is having an ID called pass, we will use this to access the password textbox.
See the code that I used here:
driver.get("https://www.facebook.com");
driver.findElement(By.id("pass")).sendKeys("pa55word");
You can see here that I used Locator ID to find the element i.e. password textbox and I have sent the character sequence i.e. the password. Hope this helps.