1 Download empty from the WordPress Plugin Directory or if you purchased a license for empty, from your account page. Afterwards you upload the unzipped empty folder to your plugins folder.

2 Log into your WordPress installation and activate the plugin empty framework through the WordPress Plugins panel.

2.1 If you have purchased an empty license switch to Empty > Updates to enter your license and activate updates.

3 Open up Empty > Settings and activate the page builder for each post type you want to use it for.
The page builder will replace the WordPress WYSIWYG editor in the edit screen of the selected post types.

4 Switch to Design > Breakpoints and enter your desired settings. To fully understand all the options have a look at this tutorial: Edit Breakpoints

5 Switch to Design > Grid / Typography and setup your desired grid system and typographic styles. To fully understand all the options have a look at these tutorials: Edit Grid & Edit Typography

6 After you've setup everything according to your needs you are finished with the configuration of empty and can now start using the page builder by creating a new page or any new post type you activated the page builder for.

To learn more about the page builder itself watch this tutorial: The Page Builder