Mode is the value occuring most of the time.
For example in a set 2,4,7,6,4,2,4,5 the mode is 2.
Median is the middle
For example 2,4,5,8,9 the median is 5. If there is even number of digits in the set, median is the average of two numbers in the middle.
Mean - Calling someone average can be mean.
For example, in a set 10,15,20 the mean is (10+15+20)/3 = 15