If you are new to theme editing, will be hard for you to edit the theme settings to add new fonts, you can use google fonts link in your global template
: <link href="https://fonts.googleapis.com/css?family=Muli:300,300i,400,400i,600,600i,700,700i" rel="stylesheet">
and then just use the font you want in css with :
font-family: 'FontName';