Here’s the most basic example which you place at the start of your child themes style.css file:

@font-face {
	font-family: FontName;
	src: url('fonts/FontName-Regular.ttf');
	font-weight: normal;
}

The above CSS rule assumes you have added your font file in a folder named fonts, in your child theme folder.

And then you simply create a new folder named fonts in your child theme folder and upload the font file to that folder.

Here’s an example of how to use a new font in your theme. This code is placed at the end of the child themes style.css file and will make all h3 sub headings use the new custom font, Adobe Garamond Pro.

h3 {
    font-family: FontName;
}