Software

If you want free, set up up the playwriting format in Word via Styles so you have keyboard shortcuts for character, dialogue, action, etc. I did this for several years with both screenwriting and playwriting because I couldn't afford Final Draft.

I do recommend Final Draft if you can afford it, though. Got it for Christmas and really like it.

Movie Magic Screenwriter is good, too!

Took me a while to tailor their Samuel French playwriting format to the true Sam French parameters in terms of tabs and such, but the Movie Magic Screenwriting program is helpful in terms of ease of formatting of stage plays as well.