Wolff works with composer. In order to use it for the first time you must have Composer installed in your machine.
You can see how to install Composer in the official page.
Once you have installed Composer, there are two ways to install Wolff:
Clone or download the Wolff repository, then open your terminal, move to your Wolff folder and run the following command:
composer install
This will download the rest of the required files and then you will be done :)
The other way to install Wolff is through Packagist: open your terminal, move to the folder where you want Wolff to be installed and run the following command:
composer create-project usbac/Wolff
This will download the whole project with everything required to run.
If you have any problem during the installation, just remember to clear the Composer cache using: composer clear-cache.
Once you're done with the Wolff installation, you should have a wolff folder, move that folder to your server root (which commonly is var/www/html or C:\xampp\htdocs).
After that, start your localhost server and go to the link: localhost/wolff. You should be able to see the Wolff welcome page :).
Another alternative is using the PHP build-in web server, move to your wolff folder and run:
sudo php -S localhost:80 -t public
Now accessing localhost should show you the Wolff welcome page.