Are these the type of icons you are talking about http://fontawesome.io/icons/ When you find the correct icon you want to use, click on it. Then it will show you the code you need to add to your site. Keep in mind you also need to import the fontawesome CSS to your site first so the icons will work correctly. http://fontawesome.io/get-started/
What I would do is download the files from FontAwesome, then upload the 2 files in the CSS folder from that Zip file into your file manager. Once it is in HubSpot copy the URL. Now that you have the URL go to Content > Content Settings, Then add this to the Site Header HTML section. <link rel="stylesheet" href="path/to/font-awesome/css/font-awesome.min.css"> and replace what is in the quotes with what you copied previously for the font-awesome.min.css file in the file manager. Now that this CSS is firing on your site you should be able to use any one of those icons by using the <i class="fa fa-id-card-o" aria-hidden="true"></i> as an example.
Are these the type of icons you are talking about http://fontawesome.io/icons/ When you find the correct icon you want to use, click on it. Then it will show you the code you need to add to your site. Keep in mind you also need to import the fontawesome CSS to your site first so the icons will work correctly. http://fontawesome.io/get-started/
What I would do is download the files from FontAwesome, then upload the 2 files in the CSS folder from that Zip file into your file manager. Once it is in HubSpot copy the URL. Now that you have the URL go to Content > Content Settings, Then add this to the Site Header HTML section. <link rel="stylesheet" href="path/to/font-awesome/css/font-awesome.min.css"> and replace what is in the quotes with what you copied previously for the font-awesome.min.css file in the file manager. Now that this CSS is firing on your site you should be able to use any one of those icons by using the <i class="fa fa-id-card-o" aria-hidden="true"></i> as an example.