Drupal Commerce is the leading flexible eCommerce solution for Drupal, powering over 50,000 online stores of all sizes.
Note: 8.x-2.x is in alpha, not yet usable for production websites. Upgrades between versions won't be supported until beta.
Use Composer to get Drupal + Commerce with all dependencies.
composer create-project drupalcommerce/project-base mysite --stability dev --no-interaction
See the install documentation for more details.