[rest] How to test REST API using Chrome's extension "Advanced Rest Client"

This seems a very old question, but I am providing an answer, so that it might help others. You can specify the variables in the second screen in the form section, as shown below or in the RAW format by appending the variables as shown in the second image.

Specify Form Variables

Specify in RAW format

If your variable and variable values are valid, you should see a successful response in the response section.