You're running Leopard according to your signature. X11 can be found under Applications, Utilities. (X11 app) Yes, it's installed but you'll need to configure
whatever application that requires it in order for the app to run correctly.
You might want to read through the X11 chapter in the BSD handbook. here.
Shop for your Apple, Mac, iPhone and other computer products on Amazon.
We are a participant in the Amazon Services LLC Associates Program, an affiliate program designed to provide a means for us to earn fees by linking to Amazon and affiliated sites.