The order in which operators are evaluated is determined by the operator precedence (see also the Remarks section).
In
$a = 2 * 3 + 4;
$a
gets a value of 10 because 2 * 3
is evaluated first (multiplication has a higher precedence than addition) yielding a sub-result of 6 + 4
, which equals to 10.
The precedence can be altered using parentheses: in
$a = 2 * (3 + 4);
$a
gets a value of 14 because (3 + 4)
is evaluated first.