Those grouping symbols are the first step in the rules developed by mathematicians long ago. If the calculations involve a combination of parenthesis addition subtraction multiplication and division then. However if we want a weaker operation to be done first it is shown in parentheses.
Do inside the parenthesis first.
However if we want a weaker operation to be done first it is shown in parentheses. Do inside the parenthesis first. In doing so the order of operations is very clear. Continue working inside the parentheses by evaluating the division 36 9.