Hi Kirandeep,
Future Method –
It is a method which runs on a separate thread in the background. It does not impact the performance of a running transaction as it carried out in a different context. We use this method for the execution of long running operation such as a web call out where we are not sure when the response will come or whether a response will come or not.
Queueable Apex –
Queueable Apex is also a way of running Apex jobs asynchronously and to make a class Queueable we need to implement an interface i.e. Queueable interface. With the help of this interface, we can queue jobs and also monitor them, this is an enhanced way of running the asynchronous process as compared to the future method.