Instructions
Install one font
For the latest and most accurate information regarding installing a font in macOS, please visit Apple's website at https://support.apple.com/en-us/HT201749.
Install many fonts
1) Open the Font Book app. One way to do this is by going to Launchpad, searching for the app, and then clicking it in the search results.
2) Open Finder.
3) Browse to the location where your font files are located that you want to install.
4) Drag and drop the font files onto the Font Book app.
Outcome
The font(s) are installed and ready for use.