The order of lighting the Chanukah candles is from left to right, always starting with the corresponding night, and then lighting the remaining nights that have passed consecutively. The last candle to be lit each night is always the “Shamash.”
The candles must remain lit for at least 30 minutes to fulfill the commandment of “spreading the miracle.” If the candle goes out before this time, it must be relit, but without reciting the blessings.