Astro's fonts guide walks through its built-in Fonts API
Astro’s own walk-through of its built-in Fonts API, and a good one. Register a font in the project config with a provider like Fontsource or Google, or point it at local files, then put the <Font /> component in the page head, and the fonts get downloaded and served from your own site. Read the part on preloading and fallback settings if layout shift has ever annoyed you.