Correlation refers to a relationship between events and uses data to show a connection. Say a person must study for exams - the more studying he or she does, the better the result should be! Correlation can then be represented on a graph - a scatter plot - which will show the relationship and that person can see whether the hard work was worth it.
The easiest way would be to use a table and, to use the above example, represent the number of study hours next to the exam results. So studying for 6 hours for maths (with a result of say 85%)but only 4 hours for English(with 65%), 2 hours for history (55%) and so on, would give a set of data. Looking at the dots, consider whether the dots are randomly arranged on the scatter plot or tend to move up from left to right or down.
In this example, the data moves up from left to right :
4hrs - 65%
6hrs - 85%
This means there is a positive correlation which means studying more goes hand in hand with higher grades. However, there may be many other factors that caused this so outright conclusions cannot be drawn. It only suggests this conclusion. Say the data had been:
4hrs - 60%
2hrs - 50%
Note how the dots appear to go down or lower to the right so there is a negative correlation, meaning that the longer a person studies, the worse he or she does!
If the results show no correlation - perhaps all three subjects have a result of 70%, this indicates that there is no correlation between studying longer and exam results.