As a professional who relies on Google Docs daily, I've found that the Extensis Fonts add-on isn't ideal for offline use on Windows PCs. Instead, turn to the official Google Fonts website—a vast library of high-quality fonts. While it won't directly integrate with online Docs, it's perfect for local installations.
The homepage showcases all available fonts, with tools to adjust preview sizes and categorize by style for easy browsing. Use the search bar to find specifics quickly.
Once you've selected a font, explore its families—varying in boldness and weight. Preview glyphs below to see character styles. Click '+ Select this style' for your choices (you can pick multiple), then 'Download All' to get a ZIP file.

Extract the ZIP in File Explorer; each family is a TTF file. Right-click and select 'Install'—it takes seconds. Now use it in local apps like word processors, Paint, or Adobe Photoshop. Note: Local fonts won't appear in online Google Docs.
Google Docs lets you expand and organize its built-in fonts by language, type, and more—revealing less common options without new installations.
Open a blank Doc, click the Fonts dropdown, and select 'More fonts'.

Filter by Scripts (language), Font types (e.g., display, handwriting), or sort by popularity and alphabet.
Google Docs supports sizes up to 400 pt—adjust as needed for bold impact.
This comprehensive guide, drawn from years of hands-on experience, equips you to master fonts in Google Docs effectively.