Parentheses and brackets ( ) [ ]
Parentheses are mainly used to separate off information that isn’t essential to the meaning of the rest of the sentence. If you removed the material within the parentheses, the sentence would still make perfectly good sense. For example:
Mount Everest (in the Himalayas) is the highest mountain in the world.
There are several books on the subject (see page 120).
He coined the term ‘hypnotism’ (from the Greek word hypnos meaning 'sleep') and practiced it frequently.
They can also be used to enclose a comment by the person writing:
He’d clearly had too much to drink (not that I blamed him).
Brackets (also called square brackets) are mainly used to enclose words added by someone other than the original writer or speaker, typically in order to clarify the situation:
He [the police officer] can’t prove they did it.
If parentheses or brackets are used at the end of a sentence, the period should be placed outside, as the final punctuation:
They eventually decided to settle in the United States (Debbie's home).
Dante testified that it was the last time he saw them [the missing coins].