Add $ \dfrac{1}{3} $ and $ \dfrac{1}{8} $ to get $ \dfrac{ \color{purple}{ 11 } }{ 24 }$.

To add fractions they must have the same denominator.
We can create a common denominator by multiplying the first fraction by $ \color{blue}{ 8 }$ and the second by $\color{blue}{ 3 }$.

$$ \begin{aligned} \frac{1}{3} + \frac{1}{8} & = \frac{ 1 \cdot \color{blue}{ 8 }}{ 3 \cdot \color{blue}{ 8 }} + \frac{ 1 \cdot \color{blue}{ 3 }}{ 8 \cdot \color{blue}{ 3 }} = \\[1ex] &=\frac{ \color{purple}{ 8 } }{ 24 } + \frac{ \color{purple}{ 3 } }{ 24 }=\frac{ \color{purple}{ 11 } }{ 24 } \end{aligned} $$