The Shulhan Aruch rules (671:5) that one must light an additional candle, called a Shamash, alongside the other Hanukah candles. This insures that any benefit one may receive from the light of the Menorah, in essence, is derived only from that extra candle, and it is therefore permitted. However, the Ben Ish Hai (Rav Yosef Haim of Baghdad, 1833-1909) cites the Kab HaYashar who holds that even the Shamash may not be benefitted from. Hacham Ovadia adamantly rejects this and explains that the entire purpose of the Shamash is to benefit from its light.
The Be’ur Halacha (Rav Yisrael Meir Kagan of Radin, 1839-1933) brings Rashi's explanation that a Shamash is lit for a "HeKera"-to distinguish. That is, it is designed to demonstrate that the candles are lit for the Misva, and the other candle, the Shamash, is for light. Even if he does not need to use the light of a candle, he must show that he has other options if the need would arise. Accordingly, he continues, since the Menorah is no longer lit on the table, but rather by the windows or doors, it is clear that the lighting is for the Misva. Therefore, technically, there would be no need for the Shamash. All the more so today, the use of electric lights shows that the Hanukah lights are only for the Misva and not for light. Nevertheless, he concludes that the prevalent custom is that everyone lights an additional candle.
There is a significant difference between the way Ashkenazim and Sepharadim use the Shamash. The Ashkenazim use the Shamash to light the other candles, and since it is used to serve the other candles, it is clearly not one of the Hanukah lights. Sepharadim, on the other hand, use candles to light the Shamash, and therefore it is not evident that the Shamash is not one the Hanukah candles. Therefore, one should put the Shamash higher, lower or off to the side of the other candles to show that the Shamash is not part of the Hanukah candles.
The Be'ur Halacha (Siman 673) points out another difference between the Sepharadim and the Ashkenazim. According to the Sepharadim, even though the Shamash is lit, one may not benefit from the candles; he may only use the light of the Shamash. Per the Ashkenazim, the Rama rules that through the lighting of the Shamash, all the candles become permitted to benefit from. In any event, it is best to refrain from benefiting from the Menorah. Benefit refers to practical uses such as reading and counting money, but it is permitted to gaze at the candle to derive aesthetic pleasure.
SUMMARY
One must light a Shamash, even if he has electric lights. One should refrain from benefiting from the Menorah but may benefit from the Shamash. The Shamash should be placed in a different position than the rest of the candles.
