The linked tutorial shows how to install Magento 1.9.x, but there have been a number of changes since the release of the 2.x series. One of those changes was to use Composer, a tool for handling dependencies for PHP projects, to install a number of PHP packages that are required for Magento.
After installing Composer, move to the root directory of your Magento installation and run:
This will download and install a number of packages to complete your installation.
You can also use Composer to completely install Magento, without the need to download the archive file manually:
composer create-project --repository-url=https://repo.magento.com/ magento/project-community-edition magento
This will require authentication with a Magento account .
Composer is a popular dependency management tool for PHP, created to facilitate installation and updates for project dependencies. It will check which other packages a specific project depends on and install them for you, using the appropriate versions according to the project requirements.