Precedence rules

Boolean operators follow conventional precedence rules NOT has highest precedence, then AND and lastly OR.
Parenthesis can be used to override the precedence rules. For example:
p AND NOT q OR u will be evaluated as follows: firstly q will be negated. Next step is to evaluate p AND NOT q. The result of this evaluation will be used in OR expression with u.
Let us take the same expression but put some parenthesis there.
p AND NOT (q OR u) now order of evaluation is different. We negate the result of q OR u expression, which is evaluated first, and AND it to p.