Step 1_ First off all you have to download the .zip file of the font you've chosen and save it anywhere in your hard disk.
Step 2_ Unzip the file. IMPORTANT: you can't use the .zip file in the Fonts folder directly, you need to unzip it before install the fonts.
Selected the .zip file and double click on it to open the folder. Then you can click on "Extract all files" or drag and drop the files inside the folder in any other place on your hard disk. if you're not able to see the "Extract all files" option, you need to instal in your hard disk an unzip tool, here some free ones: 7-zip , J-zip. Anyway you can easily find other similar tools. After installed it try againg to unzip the file. Take note, is not enough just the double click for install the fonts, you must extract and save them elsewhere before their installation.
Step 3_ Install the font/fonts.
For Windows 7 Users:
Just select the font (only one between them : .ttf, .otf or .fon) then just Right-click > Install
For any version of Windows Users:
The best and safe way would be this method:
Click the Start button, and then launch the Control Panel > Click Appearance and personalization > Click on Fonts, then click File and Install New Font. Browse the fonts you want install (select each holding down the Control key if you wish to install more then one font) and at the end click simply on OK button. Your font/fonts shoul be installed now!
Otherwise you can put the font files into the Fonts folder, usually C:\Windows\Fonts or C:\WINNT\Fonts. This is the quick way to do it, but sometime could create some problem.
Mac OS Users:
Step 2_ Unzip the file. If your browser will not automatically unzip the files you've downloaded you need un utility like Stuffit Expander . While holding down the control key click on the .zip file and select the option: Open With > Stuffit Expander or just drag the .zipped file on to the Stuffit Expander icon on the Desktop.
Step 3_ Install the font/fonts ( you can install only .ttf and .otf formats).
For Macintosh OS X 10.3 or above (including the FontBook) Users:
Just Double-click the font file > "Install font" button at the bottom of the preview.
For any version of Mac OS X:
If you need to share the font with all users put the files into /Library/Fonts. If the font is only for you put the font into/Users/Your_username/Library/Fonts.
For Mac OS 9 or earlier:
Some formats are not supported to these version, so if you need you can convert them in the ormat you need with utility like TT FontConvert. Then drag the fonts suitcases into the System folder. Will come up a window asking you if you want them installed. Click 'OK' to add them to the Fonts folder. Now simply restart your Mac.