When transcribing a document or an item from a document, use brackets to indicate when you are “guessing” at a word or phrase or adding a word or phrase of your own. Personally I add words or phrases rarely, preferring to comment later if something warrants it. The word sic (Latin for “as is”) should be bracketed as well when it is used to indicate that you copied something exactly as it was in the document–even though it looked wrong. For example, “…to my son[sic] Elizabeth I leave my farm…”  
Get the Genealogy Tip of the Day Book