Web Pae Diagnostic

I was trying to use the web page diagnostic of load runner to diagnose the problems in my web site. I had a problem analyzing the Client time. does anyone know what the exact meaning of this time is?
Also in the "Time to First Buffer Breakdown Graph " we can see that there has been a comparison in Network and Server time. But I believe that it doesn't give me the exact Server time. does any one know how I can analyze the server's time exact time?