the first line estalishes a relation between any bindable action inside wow and any key one chooses. but this is volatile, it just resides inside that running wow instance you typed that command into.
the second line tells wow to permanently save the current key configurations ( which you just changed ) to a file ( /wow/WTF/<accname>/bindings-cache.wtf ).

so you have to type this in only once per wow-installation and it will be permanent until you rebind that key or delete your WTF folder orsomething like that. you do not necessarily have to create a macro for this purpose.
you do not even have to type this ingame, you may as well just edit your /wow/WTF/<accname>/bindings-cache.wtf manually ( just add the line bind L TURNORACTION and you're done ).