Upload via ftp the *.ttf font to a location on server, for example /var/www/website/wp-content/themes/fonts/
Once the file is uploaded add to the stylesheet (style.css) the following:
@font-face {
font-family: Custom Font;
src: url(http://www.yourwebsite.com/wp-content/themes/fonts/custom-font.ttf);
font-weight: normal/italic/bold;
}
Call it where needed:
.h1 site-title {
font-family: "Custom Font", Arial;
}