Try typing just "composer" if you get a list of available commands to see if it works.

Also after laravel/laravel you should specify a directory with a dot (.) meaning install in current directory or write a folder name which will be created.

composer create-project laravel/laravel MyProject --prefer-dist

If you're using Composer locally in your project, you want to use php composer.phar rather than composer. You can make composer available globally with mv composer.phar /usr/local/bin/composer, assuming you have /usr/local/bin in your $PATH.

You can also try using the full path to your composer.phar file.

/path/to/composer.phar create-project laravel/laravel MyProject --prefer-dist