In the Vars tab > Pre Request variables section, you can write any strings, numbers or any valid JavaScript literal. This is useful for setting variables that will be used in the request before it is sent.
In the Vars tab > Post Response variables section, you can write any valid JavaScript expression. The res object is available, allowing you to declaratively parse the response object and set variables, instead of writing scripts to do the same.For parsing the response, you can checkout the response query that allows you to easily query your response.