Finding a monitor for a old Powermac is really not much different than trying to do the same thing with a newer computer. With an older computer…you may or may not need a video adapter.
You need to figure out what video port your PowerMac has…get the proper cable…and then connect everything up.
Many monitors have multiple video ports (VGA, DVI, HDMI, etc.). You would probably use the VGA port on the monitor for your Powermac.
As you probably know…a Powermac 7200 is a "Ye Very Old Computer". It is probably worth about $15 dollars. So please don't spend a ton of $$$ on a monitor. Get one for free somewhere…or an inexpensive one via Craig's List.