Analyze Response Time Graph in jmeter

I am new to jmeter and don't know proper meaning of Request Time Graph that is being generated after I send requests from jmeter.My thread properties is mentioned below :

Number of Threads : 500 Ramp-Up Period : 1 Loop Count : 1

I am able to generate Response Time graph and picture of that graph but not able to get the proper meaning of this graph. I am attaching graph image below : Response Time Graph