Is it possible to install the dependencies you have in composer.json file without you have composer as tool in you machine?

Question

I'm trying to put this app working but unfortunately whenever I try to install all dependencies inside composer.json file as you can see in the image above I'm getting that error. I don't know what's going on, I don't have composer installed as tool itself for dependency management in PHP. Is it that are causing this error?

*PHP 7.1 is the version of PHP that I'm using.