We will learn some relevant concepts using a simple example. 15 students took a 5question test that required either true or false as answers.
The scores could be:
2 1 3 4 4 3 3 4 3 5 4 4 5 4 4
We could first tally the results.
Number of Correct Answers.  Frequency 

0  
1  / 
2  / 
3  //// 
4  // 
5  // 
The data could also be arranged into a table called frequency distribution/table.
Number of Correct Answers  0  1  2  3  4  5 
Frequency  0  1  1  4  7  2 
Next, we could also represent this data graphically using a bar chart.
Mode is the observation value that occur with the largest frequency. In our example above, the mode is 4.
Use of GDC. Once finished then press [2nd][MODE] for quit. Before you plot your histogram,
make sure there is no function in [Y=] because they will interfere with
your plot latter. Before you plot, make sure that you set your [WINDOW] to match your data.
In the example above, we could have Xmin=1, Xmax=7, Xscl=1,Ymin=0.5,
Ymax=8,Yscl=1,Xres=1. 
Exploration:
A group of teachers had been surveyed about their daily consumption of coffee (measured in cups). The frequency distribution is as below:
Number of cups  1  2  3  4  5 
Frequency  7  3  5  0  1 
The shape of a distribution.The example here is a distribution that is negatively skewed. That is there is a long tail at the lower (negative) end of the distribution. 
The distribution is positively skewed if there is along tail at the high (positive) end of the distribution. Here, we have a distribution represented by a vertical line graph.

If all the bars are of the same height then we have a uniform or rectangular distribution. 
If the shape of the distribution is symmetric and bellshaped then it is known as a normal distribution. 