How to install Composer to use Ratchet ?

I finaly tryed to execute

Code:

composer require cboden/ratchet

shown in the tutorial https://c-mh.fr/posts/websockets-en-php-...n-y-parait

This let me understand that I need to install Composer.
I did that with

Code:

apt install composer

(I am running Ubuntu).

After that step done,

Code:

composer require cboden/ratchet

, I am confused.

The tutorial says :

Si votre projet est vierge de tout contexte "Composer", l'outil va vous demander diverses informations pour créer votre fichier "composer.json". Si tel est le cas, exécutez ensuite la commande suivante :

Google translation :

If your project is blank of any "Composer" context, the tool will ask you for various information to create your "composer.json" file. If this is the case, then run the following command : composer install

I dot not know if my brand new CI is blank or not of any "Composer context", how can I check this ?

Do I have to run, or not

Code:

composer install

?

Note that, the command

Code:

composer require cboden/ratchet

did not ask me anything to create the composer.json file.

Thank you for helping,
Nils