Multiplication is just repeated addition. Remember that.
Say you have \(x\) processes, from which each process have \(y\) different outcomes. If you need to choose one of the \(x\) processes and do that process, then from the adding rule, the number of possible outcomes is then
\begin{align} &=\overbrace{y+y+y+\dotsb+y}^{\text{\(x\) times}}\\ &=xy. \end{align}
For example, if you had five differently coloured fair dice, and you had to roll one of them, then you can get any one of the \(5 \times 6 \) outcomes if you take the colour of the die into account. For example the outcome could be (red,3).
We can multiply because for every one of the \(x\) processes, there is an addition of \(y\) outcomes. Hence there are \(x \cdot y\) total number of outcomes.