A bell shaped curve on a graph is symmetrical and has no skew. The peak of the graph is in the centre and the tails either side of the peak are a mirror image of each other. The mean, median and mode are all in the same position on the graph (right through the centre of the peak).
When a graph is said to be skewed, this refers to the tail and not the peak of the graph. In a left skewed graph (also known as a negative skew) the mean is to the left of the median, whereas in a right skewed graph (also known as positive skew) the mean is to the right of the median, as can be seen below: