It's better to make a copy of "theme" directory from downloaded package. So you still have pre-designed templates untouched.
Open /assets/js/script.js file and set the configuration options if you'd like. There's possibility to set your Google API Key, Google Analytics Tracking, and choose to have smooth scroll or not. The script.js file has a complete documentation to help you configuring your template.
If you're going to have a contact form in your website, you should make some more configurations. Please open /assets/php/sendmail.php files and configure your contact form with specifying your email address and default subject.