By default the Total theme uses the system UI stack for the site font which is the fastest font because it will use the native font of the visitors computer/device. To change the default font family used across your entire site you can do so easily via the theme’s Typography settings.
Simply go to Appearance > Customize > Typography and click on the Body tab so you can modify your font family. In web design the website’s “body” is basically the entire site so when you target your body settings it’s going to target all elements on the site.
Now, if you change the other settings such as the color and font size, these options are going to modify your site “text” so if you want to modify the color and size of other elements (like headings) you’ll want to click on their respective Typography tab.