On which side of the menorah does the shamesh go if it is not in the center and in which order to light. Thank you.
The shamash only needs to be noticeably separated from the other candles. It doesn't need to be in the center or on the side, even. I have a menorah which has a back panel and the shamash hangs from the top above and behind the other candles.
When facing the menorah, you place the candles from right to left. Meaning, the 1st night the candle is on the right; 2nd night has 2 candles - one on the right and 2nd to its left. Continue in this fashion each night.
Lighting goes from left to right. I.e. the newest candle is always lit first.
O.C. 673:1 Originally, an extra candle was used and placed a distance away from the rest of the menorah. Currently, people just place this candle to the side. Ideally, the shamash should be longer than the other candles. The point is, that this candle should be recognizable from the rest of them, either by length or by separating them from the rest.
O.C. 676:5 details how to arrange and light the candles.