the mean is the average of a set of numbers; to calculate it, you take the sum of each of the terms in the set and then you divide that sum by the total number of items you have in your set.

the mode is a number in a set that occurs most often.
 
the median is the middlemost number in a set of numbers if the set is arranged in order.

(1) What is the mean of this set of numbers: {2, 3, 4, 5, 6, 7, 3, 2, 3, 4}

(2)  What is the mode of this set: {2, 3, 4, 5, 6, 7, 3, 2, 3, 4}

(3)  What is the median of this set: {2, 3, 4, 5, 6, 7, 2, 3, 4}