how do i install X11 on my macbook pro

https://www.xquartz.org

This is an X11 Display Server, and a few X11 apps in /opt/X11/bin/.

If you are going to send Unix/Linux displays to your Mac, then install XQuartz and Logout of your session or reboot (which will effectively log you out).

After logging back in, you can use

ssh -Y username@remote.Unix.or.Linux.address

--OR--

ssh -X username@remote.Unix.or.Linux.address

This will export a DISPLAY environment variable to the remote system so that any X11 based app you start over this ssh connection will display back on your Mac. It will look something like the following:

$ printenv DISPLAY
localhost:10.0

If your remote systems has shell initialization scripts that override the DISPLAY environment variable, then you should disable that in your remote shell initialization scripts.