Soft line wrapping is activated with Meta-$.
Wraps lines without inserting line break characters into the file.
That is, the effect is purely visual.
Hard line wrapping is activated with Meta-L.
Wraps lines by inserting line breaks into the file.
The file is physically changed.
META:
Note on keystroke notation -
if you are new to Linux, the notation Esc+$ means press and release Esc
and then press $. The full key press sequence then is Esc, Shift+4.
(It does not mean hold down escape while pressing $.)