In many places in your course pages, you'll have the option to directly customize your fonts with a single click.
In Step 4, when you customize a page and edit a Column, look for the gear icon here:
Click the gear icon, and you'll see an option to add the font of your choice
Note that not every single text field in the course can be customized in this way - if it IS available for the text field, you'll see the gear icon when you edit the column.
You can also customize the fonts in your site using CSS coding (as long as you're on the Growth Level Plan or higher).