The correlation will always have values between -1 and 1. The closer to either of -1 or 1 the value is the more there is evidence of a strong relationship between the 2 groups. So, the closer the correlation is to 0, the less of a relationship between the 2 groups. Correlation of 1 indicates that there is a positive correlation - ie: when the values of 1 group increase, the values of the other group increase or if 1 decreases then the other tends to decrease too. A correlation of -1 is the opposite - that is: when 1 group increases, the other decreases and vice versa.
A value of 0.556, as u can see from the scatter plot, indicates that the values are indeed somewhat related. The closer to 1 the correlation is, the closer to a straight line the scatter plot will be. So, in conclusion, there is enough evidence to warrant doing more tests to between these 2 groups.