Thank you for writing in, to add a Google Font, first navigate to https://fonts.google.com and search for the font that you need (example: Niconne). Hit the add button that correspond to it.
You should then able to see a number of font-family selected on the bottom panel. Expand that panel and click the @IMPORT tab. Then copy just the line:
Yes, do not include the
<style> and </style> tag.
Then paste that
@import line statement on top of your child theme's style.css file
Then to apply the font-family; define this class, on child theme's style.css file or Theme Options > CSS
font-family: 'Niconne', cursive !important;
Then apply that class to your text or headline element.
Hope it helps,