As I alluded to earlier, installing Drupal 8 is best done via the Composer template project. However, you may also install it straight from Git by checking out the latest tag or commit in the Drupal.org Git repository (https://www.drupal.org/project/drupal/git-instructions). If you do this, you will need to install its dependencies via Composer, and Drupal has many.
To this end, you will need to have Composer available on your development environment and have a basic understanding of how to use it.