There is an app called Atlassian REST API Browser (RAB) that you can install in Jira that allows you to interact with your Jira's REST APIs directly in a browser. You can get this app from https://marketplace.atlassian.com/plugins/com.atlassian.labs.rest-api-browser/server/overview.

After you have installed the app, you can open your browser and go to http://your_jira_instance/plugins/servlet/restbrowser. You should see an API browser interface similar to the one shown in the following screenshot. On the left-hand side, you will see a full list of the REST APIs that are available in your Jira instance (based on its version):

When you click on any of the APIs, the browser will present you with all the parameters and options available, so you will no longer need to manually find out what they are. This allows you to test and experiment with the APIs quickly, without having to write any code upfront or use any additional tools.