I won’t go into too much detail to explain what YeoPress does but you can read more about it from the creator himself, Wesley Todd. YeoPress: A Yeoman Generator for WordPress, basically installs WordPress via the Command Line/Terminal. It’s also assuming that you’re working locally (which is a good start for developing WordPress themes). So you still need to create your database and you have to know what your database username and password will be (this is to set up your wp-config.php file) For example: Database Username: root, Database Password: empty). Be sure to check your database privileges for editing access too. The steps described by Wesley are easy to understand and the instructions set up are pretty straightforward.