option to add a 2nd screen for my Mac Pro (2019)

If this is a silver tower Mac Pro, you just plug the display cable directly into one of the several ports on the graphics card, or use a USB-C port with adapters.

If this is a MacBook Pro, (¿what screen size?) you can directly run a USB-C or Thunderbolt Display, and run HDMI, DVI, or VGA displays by using adapters or adapter/cables.

¿what make&Model display, or a link to its specs?