One of the very popular REST clients is Postman. Postman is a Google Chrome app. If you are using Chrome, then you can install this app from here: https://chrome.google.com/webstore/detail/postman/fhbjgbiflinjbdggehcddcbncdddomop/related?hl=en.
Once you open Postman, you will be able to select the method as POST or any other method and, on selecting the Body tab, you will be able to set field names and values and then hit Send. Check the following screenshot of Postman having fields set and the responses. This will give you an idea about how Postman can be used for post requests:
You can see the POST request has been sent through ...
