Install your font

Find the file you just downloaded, usually in Downloads.
Double-click it. Font Book opens and shows your letters.
Click Install Font.
Open any app and pick it from the font menu. Already-open apps need restarting first.

It didn't work

Restart the app you are trying to use it in. Most only read fonts at startup.
Check the file downloaded fully. A part-downloaded font will not install.
On a work laptop, font installation is sometimes blocked by your IT department.
Google Docs cannot use custom fonts. Not yours, not anyone’s. It runs in the cloud and only offers its own list. Use Word, Pages or Canva instead.
Canva needs a paid plan to upload fonts. Uploading lives in the Brand Kit, which is a Canva Pro feature. CapCut has no such limit.