How to install a font
Under Windows 10/8/7/Vista
Select the font files (.ttf, .otf or .fon) then Right-click > Install
Under any version of Windows
Place the font files (.ttf, .otf or .fon) into the Fonts folder, usually C:\Windows\Fonts or C:\WINNT\Fonts
(can be reached as well by the Start Menu > Control Panel > Appearance and Themes > Fonts).
Under Mac OS X 10.3 or above
Double-click the font file > "Install font" button at the bottom of the preview.
Under any version of Mac OS X
Put the files into /Library/Fonts (for all users),
or into /Users/Your_username/Library/Fonts (for you only).
Under Mac OS 9 or earlier
The old Mac fonts are not supported anymore at dafont. First, you have to convert the font files (.ttf or .otf) you have downloaded.
Then drag the fonts suitcases into the System folder. The system will propose you to add them to the Fonts folder.
How to install a font under Linux?
Copy the font files (.ttf or .otf) to fonts:// in the File manager.
Or: Go into the /home folder, in the menu select View > Show Hidden Files, you will see the hidden folder .fonts (if not, create it) then copy the font files there.
Linux versions - Ubuntu
Double-click the font file > "Install font" button in the preview window.