Fonts
A few text styles your whole brand draws from.
Your brand defines a few text styles: a heading, a subheading, body text, and a button. Each one sets the font, the weight, the letter spacing, and whether it's uppercase. Every piece of text in a creative uses one of them.
How text uses them
A piece of text doesn't carry a font. It carries a name, like heading or body, and your brand decides what that looks like. So changing your heading font in your brand updates every heading everywhere, and clearing a font on one element brings back the brand default for its style.
Beyond the basics
The four styles cover most needs, and a few friendly names map onto them on their own: a "headline" uses your heading style, a "caption" uses body. A template can also invent its own named styles, like "hashtag" or "quote", as long as the brand or template says what they look like.