Magento 2 Installation Fatal Error - Cannot instantiate interface

Make sure the PHP module intl is installed, clear var/generation (or generation/* if you're using Magento 2.2+) and var/cache, enable Magento modules (bin/magento module:enable --all), compile DI (bin/magento setup:di:compile), and then try again.

If you use nginx configuration from the official sample and running Magento in the default/developer mode this situation might happen with document root global value set as

root $MAGE_ROOT/pub;

The issue can be fixed by setting Magento root from pub directory to the root index.php

root $MAGE_ROOT;

In case of Apache the DocumentRoot value change might also fix the situation. Hope it will help.

After you downloaded all the files/created the project through composer, you must setup the store. You can do this from the command line:

php bin/magento setup:store-config:set --help

Or going to: http://mystore.com/setup