There are two ways you can install a font on your Mac device!
Below are step by step instructions for both ways.
First - for both install ways you will need to locate the font in your downloads folder using the finder: 
Next, for the first way of installing - all within your downloads folder follow these steps: 
1. Right click on the font you wish to install - we are installing NA Silly Safari - OTF.
2. Hover over "Open with" and press "Font book" 
3. A New popup will appear, click "Install Font"
That's it!
The second way to install fonts onto a Mac device is through the Font Book app directly:
1. Open your font book app
2. Press the plus sign in the top bar
3. Click 'Downloads'
4. Locate the font or fonts you wish to install (when installing multiple fonts in the same folder, you can hold down your command key to select multiple items!) - click to highlight the font(s)
5. Press "Open"
These will install to your device!
Restart your programs, and enjoy your fonts!