From our example where we take the sum of two die, the outcome A = { 4,5 } from the collection S = {2,3,4,...,12} would be
\begin{gather*}
|A| = | \{ (1,3),(2,2),(3,1),(1,4),(2,3),(3,2),(4,1) \}| = 7\\
|S| = | \{ (1,1),...,(1,6),(2,1),...,(2,6),...,(6,1),...,(6,6) \}| = 36
\end{gather*}
and so the expected relative frequency would be |A|/|S| = 7/36. Compare this theoretical value with the sum of the two outcomes from your experiment above.