I have been using Jmeter to simulate backend but I have not used the aforementioned elements. Do I need to use them? Would that make my Jmeter script better and more realistic? Please explain with Examples?
HTTP Cookie Manager - represents browser cookies. You will need it to deal with cookie-based authentication and to mimic real user sessions starting from login so the whole business process will be performed by the same JMeter thread which represents virtual user which in their turn should be as close to real users as possible
HTTP Cache Manager - required to represent browser cache. Real browsers are downloading embedded resources like images, scripts, styles, etc. when they request web pages. However well-behaved browsers do it only once, on subsequent requests aforementioned images, styles, etc. are being returned from cache and no actual requests are being made to the server.
See How To Make JMeter Behave More Like A Real Browser article for more detailed explanation of above Test Elements and few more tips on how to make your test more realistic.