How to make Curl and PHP available when installed from Xampp
What it means is that you don't have curl installed and you need to install curl to use it. This can be done by going to a terminal CTRL + ALT + T then entering sudo apt-get install curl libcurl3 libcurl3-dev php5-curl. This will install curl, php and the necessary libraries to provide you with the functionality that you need.
After the installation has completed, restart the server with sudo service apache2 restart