<link rel="stylesheet" href="https://use.fontawesome.com/releases code example

Example 1: font awesome icons cdn

To load all styles:

<link rel="stylesheet" href="https://pro.fontawesome.com/releases/v5.10.0/css/all.css" integrity="sha384-AYmEC3Yw5cVb3ZcuHtOA93w35dYTsvhLPVnYs9eStHfGJvOvKxVfELGroGkvsg+p" crossorigin="anonymous"/>

Example 2: fonawesone cdn

<link rel="stylesheet" href="path/to/font-awesome/css/font-awesome.min.css">