This question already has an answer here:
According to the Emacs tutorial:
Type M-x auto-fill-mode now. Then insert a line of "asdf " over again until you see it divide into two lines. You must put in spaces between them because Auto Fill breaks lines only at spaces.
In other words, Emacs will automatically create a new line after a certain threshold.
How do I do the same in Vim, and how can I do this with already written text?