All I want to do is write script for a play, I a new with the Mac PC HOW CAN I DO IT.

Are you looking for a specific script-writing application, that understand the formats for plot, scenes, actions, etc., or just a general text-writing application.

At its simplest level, your Mac comes with TextEdit, a simple text editor. You can also install Pages from the App Store for a more full-featured text app, or search the App Store for 'script writing' to see a slew of other applications that may be more full-featured.

Scrivener or an alternative, or maybe a cloud-hosted script-writing hosting service if you’re inclined.