Using automatic hyphenation
TextEdit does not initially hyphenate words for you. A new line of text is broken off at the end of a whole word.
If you prefer to use hyphens to break up a word at the page margin, TextEdit can do this automatically.
Choose Format > Allow Hyphenation.
To turn automatic hyphenation off, choose Format > "Do not Allow Hyphenation." Regardless of the setting you choose, you can always hyphenate specific words using the hyphen key.