How to use and send POST method and what software to use

POST is just an HTTP request type - GET, HEAD, POST, PUT, DELETE, etc

You can use a plugin like RESTer for Firefox, or any number of the others, to make the POST request. You’ll have to find the right headers to include to log in (assuming you’re talking about a level on here), otherwise it won’t work. You’ll need to research authentication options, both configuration settings for your tool and different ways to authenticate to sites.

You can also use curl, like Kernel_Junky said, but, again, you have to do some research on the various options there. Get comfortable using cURL to download files, log in to websites, etc.

You can also use programming libraries to do this, but, then you’re solving multiple new problems at one time.

Check out https://docs.postman-echo.com/?version=latest as a starting point. You’ll be able to learn what works and doesn’t work, and how and kind of why.