Often the easiest way to find the RTSP details for your system is to contact your CCTV installer or operator, they should be able to provide you with all details you need.
RTSP URLs vary between manufacturer, you can find their structure in the user manual for your specific camera.
Here's an example URL:
Let's break that down:
rtsp:// - tells us that we are accessing an rtsp url
username - will be the username set to access your camera
password - the password set to access the camera
@192.168.0.50 - this is the IP address of the camera on your network
:554 - is the standard port number used for RTSP
/Streaming/Channels - is part of the url that this manufacturer uses
/1 - this is selecting the primary video channel for the camera
The username and password will either be set during installation for the camera, or they could be left as the default.