PHP GPM Problem

Hello,
I'm very new to this, so I apologise if this is something simple.
I have downloaded SoraArticle skeleton and have it running in :-
C:\xampp\htdocs\grav-sora

This works fine. I now want to add some plugins, and so have been attempting to use GPM.
I have installed PHP, and set the PATH. If I open CMD inside the grav-sora folder, I can type 'PHP -v' and I get:-

'PHP 7.1.1 (cli) (built: Jan 18 2017 18:38:28) ( NTS MSVC14 (Visual C++ 2015) x64 )
Copyright (c) 1997-2017 The PHP Group
Zend Engine v3.1.0, Copyright (c) 1998-2017 Zend Technologies'

If I then type 'php grav/gpm index' as per the help file, I get :-

'Could not open input file: grav/gpm'

What am I doing wrong?
Thanks,
Matt.

Note, that when in the right directory in the console, the command is php bin/gpm or php bin/grav. There is no subfolder of Grav called Grav which contains the GPM.

Thanks.
php bin/grav now works fine.
However php bin/gpm gives me the following error:-

FATAL: GPM requires PHP Curl module to be installed

I'm assuming that this would be a separate download and installation from somewhere?

Curl is something commonly included with PHP, see this page in the docs to verify that it is enabled. Generally you'd only need to un-comment it in php.ini.