You don't need to use it when are a beginner. A parenthesis is an "aside." It is something extra. It is something that could be left out, without changing the grammar or the MAIN meaning of the sentence. A "parenthesis" is also the name for a punctuation mark. This is a "left parenthesis:" ( This is a "right parenthesis:" ) (This sentence is within parentheses.) When the marks are not used, it may be called a "parenthetical phrase." I am going to add a parenthetical phrase to a sentence: 1) "All children grow up." 2) "All children, except one, grow up." "Except one" is a parenthetical phrase. I am going to give an example of parentheses within a sentence. 1) "Each in her turn cleared her throat, held up her manuscript, and proceeded to read." 2) "Each in her turn cleared her throat, held up her manuscript (tied with dainty ribbon), and proceeded to read." "Tied with dainty ribbon" is an extra detail. It adds something to a sentence that makes perfect sense without it.