We normally recommend people just use a Google font that is available in the theme. Some people use webfonts purchased from myfonts, fonts.com, typekit etc which requires adding a link to the head section of the site and then some lines of css.
However to upload your own font you would need to create the css file with @fontface to set up the fonts, then to assign them you would need to add this to your custom css:
/* BODY FONT */
body,p {
font-family: "museo-slab"!important;
}
/* HEADING FONT */
h1, .impact-text,.impact-text-large {
font-family: "museo-slab"!important;
}
h2,.blog-item .quote-excerpt {
font-family: "museo-slab"!important;
}
h3 {
font-family: "museo-slab"!important;
}
h4 {
font-family: "museo-slab"!important;
}
h5 {
font-family: "museo-slab"!important;
}
h6 {
font-family: "museo-slab"!important;
}
/* MENU FONT */
#main-nav, #header nav, #vertical-nav nav, .header-9#header-section #main-nav, #overlay-menu nav, #mobile-menu, #one-page-nav li .hover-caption {
font-family: "museo-slab"!important;
}
– Kyle