A period marks the end of a declarative or an imperative sentence. It is followed by a single space (not two spaces). It is sometimes used at the end of an incomplete sentence.
Example: The storm was almost upon us, so we needed to take shelter.
Incomplete: Under a tree perhaps.
When an entire independent sentence is enclosed in parentheses or square brackets, the period belongs inside the closing parenthesis or bracket. When a clause or even a complete sentence is enclosed within another sentence, the period belongs outside.
Example: Sharon rewrote her manuscript over and over. (She never tired of editing.)
She said she would never speak to him again [referring to her former boss].
When quoting Scripture, the citation goes in parentheses and the period goes at the end. Example: “For God so loved the world that he gave his one and only Son, that whoever believes in him shall not perish but have eternal life” (John 3:16 NIV).
No period should follow chapter titles, subheadings, column headings in tables, dates, signatures, or addresses.