driver = webdriver.Firefox(...) # Or Chrome(), or Ie(), or Opera()
username = driver.find_element_by_id("username")
password = driver.find_element_by_id("password")
username.send_keys("YourUsername")
password.send_keys("Pa55worD")
driver.find_element_by_name("submit").click()
Notes to your code:
find_element_by_name('Username')
: Username
capitalized doesn't match anything.Select()
is used to act on a Select Element (https://developer.mozilla.org/en-US/docs/Web/HTML/Element/select)