Whenever we add or subtract fractions, we have to first ensure that the denominators of the fractions are the same. In this case, they are, so we don't have to go out of our way to find a common denominator.
[tex]\dfrac{3}{5}+(-\dfrac{1}{5})[/tex]
Now, let's open up the parentheses:
[tex]\dfrac{3}{5}-\dfrac{1}{5}[/tex]
Subtract only the numerators:
[tex]\dfrac{2}{5}[/tex]
[tex]\dfrac{2}{5}[/tex]