To get started:
• Follow the link to Google Fonts and download a font and place the unzipped font into the fonts folder.
• Create a folder and name it css.
• Open the folder and inside create a file and name it fonts.css.
• Open the fonts.css file and add copy/paste the following into it.
• Change the name of the font AbrilFatface to the font you are adding.

@font-face {
font-family: AbrilFatface;
src: local(AbrilFatface), url(../fonts/AbrilFatface.ttf) format('opentype');
}
.abril {
font-family: AbrilFatface;
}

Be sure to add the following into the top of your style sheet.

@import url('fonts.css');

Open the file where you have the TinyMCE scripts and add the following.

font_css: '../css/fonts.css',