How to fix an error when installing Composer'a?

Question

PHP

There was a need to use the instagram-php-scraper library ( https://github.com/postaddictme/instagram-php-scraper)
1) downloaded
2) downloaded php ( windows.php.net VC11 x64 Thread Safe (2017-Jan-19 07:07:56))
3) Installed on C: \ php
4) Downloaded vc_redist.x64.exe installed
5) downloaded composer.phar and zayuzat php composer.phar install and even downloaded then just composer and installed
6) In the instagram library -php-scraper has composer.json file
7) trying php composer.phar install or composer require mashape/unirest-php
Error
composer require mashape/unirest-php
Using version ^3.0 for mashape/unirest-php
./composer.json has has been updated
Loading composer repositories with package information
Updating dependencies (including require-dev)
Your requirements could not be resolved to an installable set of packages.
Problem 1
- mashape/unirest-php v3.0.4 requires ext-curl * -> the requested PHP extens
ion curl is missing from your system.
- mashape/unirest-php v3.0.3 requires ext-curl * -> the requested PHP extens
ion curl is missing from your system.
- mashape/unirest-php v3.0.2 requires ext-curl * -> the requested PHP extens
ion curl is missing from your system.
- mashape/unirest-php v3.0.1 requires ext-curl * -> the requested PHP extens
ion curl is missing from your system.
- mashape/unirest-php v3.0.0 requires ext-curl * -> the requested PHP extens
ion curl is missing from your system.
- Installation request for mashape/unirest-php ^3.0 -> satisfiable by mashap
e/unirest-php[v3.0.0, v3.0.1, v3.0.2, v3.0.3, v3.0.4].
To enable extensions, verify that they are enabled in your .ini files:
- C:\php\php.ini
You can also run `php --ini` inside terminal to see which files are used by PH
P in CLI mode.
Installation failed, reverting ./composer.json to its original content.
Can you explain how?

Answer 1

the requested PHP extension curl is missing from your system

what is unclear here?