Researchers used the Independent Samples T-test with two tails to see if there were statistically significant differences in self-esteem levels between boys and girls. This test type is used to compare mean differences on continuous variables between two groups. Independent samples t tests assume that the two groups are of equal variance, but this may not apply in this study because there might be different variances between girls and boys.
They first determined the average level of self-esteem in each group. Then, using the independent samples t test, they compared this mean. Assuming that both sets of data were normally distributed (i.e., bell shaped curve), they could calculate a p value to identify whether or not there was a statistically significant difference between them (p<0.05). If the p value turned out to be less than 0.05, then we can conclude that there is indeed a statistically significant difference in self-esteem levels between boys and girls, but if it turns out to be greater than 0.05 then we cannot make any conclusions about their difference since it would suggest that their means are not significantly different from one another at α level 0.05