The Network Client is used to view live or recorded video from Analog or IP cameras. With the client you can view cameras from multiple servers side by side on the same screen.
If you are able to see live video, but the left tree navigation does not expand to show recorded video you are most likely in Multiple Database Mode. You will need to switch to Single Database Mode. To switch to Single Database Mode, go to Setup/ Network Client/ Database/ Single Database and check the option for "Use Single Database Mode" and restart the Network Client.