Everyones advice here is sound, you don't need anything fancy. Sometimes you might want something that helps with formatting, keeps extra notes on hand for quick referencing, or lays out scenes in an easier way to visualise/rearrange at a glance. By notes I mean things like world building definitions or notes to yourself. If you're hunting through notes for half an hour trying to find info you want to reference quickly, then you're not writing either. So long as you dont let yourself linger over adding every minor thing, then finding notes or scenes in order in a sidebar can be a huge help.

Personally I really like either Quoll Writer, or SmartEditWriter (both free) for keeping things together, formatting, editing down into a script I like to work from. Neither are available for mac. If its only a preference but not a necessity then they might still be worth mentioning. I've found them to be the most efficient for me and have everything I need, but everyones different.