6.5.3.7 Breaking or Joining Lines

To break a line without affecting text, move the cursor to a space where you want the line to break and type r (for "replace") followed by Return. Note that if you type r with the cursor on a character and then press Return, that character will be replaced by the Return.

To join two lines, place the cursor on the upper line and type an uppercase J. (There's no need to press Esc after typing J.)