Scratch is a starter theme generator based on _s and Foundation. It's a theme meant for hacking so don't use it as a Parent Theme. Instead try turning it into the next, most awesome, WordPress theme out there.
Make sure you have the following installed:
In the root of the repository, run the following:
# Install composer dependencies
composer install
# Install grunt dependencies
npm install
# Build the project
grunt
In your wp-content/themes folder you will now have a folder with the name of your theme which is setup with the basics to get a theme off the ground quickly. In the root of your newly created theme you'll have the following grunt tasks you can run:
# Run the default tasks that build the project
grunt
# Initiate Browsersync and watch files for changes
grunt server