You can get scent bars that melt in with the wax or you can add candle fragrance oil. Be careful that you don't add too much, since it can affect the structural integrity of the candle.
I bought the scent bars at Michaels, I think. Otherwise you could check Amazon. I prefer using oil since it's one less thing that has to be cut and melted.
Is fragrance oil very different from essential oil, or could you also use essential oil? My guess is that essential oil does not have a strong enough scent. You would have to add so much to make it really smell.
Essential oils are extremely potent, actually, so you would probably add less to get the desired scent. I haven't tried adding them to scent candles, though, so I don't know how well they work.