You need to use the Google reference guide for the translate method.

https://cloud.google.com/translate/docs/reference/translate

The request is a simple POST with a couple of query string parameters.

• q: the input text you want to translate
• source: the language of the input text (e.g. en for English).
• target: language to which you want the text to be translated (e.g. ja for Japanese)
• format: the format of the input text ("text" for plain-text, and "html" for HTML)
• key: your API key you generated in the earlier step.

Next: Using Postman to Test Your HTTP Request