You can add Google Font link tags to one or all pages in your settings, or in the header HTML field. If you're comfortable editing CSS, you could add the @import code to the top of a specific CSS file.
Please note: if you're creating content using a theme, you can choose any Google Font directly within your theme settings. All Google Fonts are also supported in starter templates in the Design tab.
Copy your Google Font's Script
First, copy the script for your desired font from Google Fonts.