Macs running OS X Yosemite have a native font management tool called Font Book. To add a new font to your Mac, download the desired font, open it in Font Book and click "Install Font" to make the font available to all compatible applications on the computer.
Click the "Finder" icon on your Mac's dock to launch the Finder.
Click your home user account folder on the menu on the left of the Finder window and select "Downloads" to view your recent downloads.
Double-click the downloaded file to extract its contents and then click the folder containing the extracted files. Some fonts are not contained in folders and will be directly clickable in your Downloads folder after you extract them.
Click the font file to open it in Font Book.
Click the "Install Font" button to add the font to your Mac.
You can also install fonts from within Font Book. Click the Applications folder on your Mac’s Dock or in the Finder to view a list of applications installed on the computer. Click the “Font Book” icon to launch Font Book. Click “File” on the main menu and choose “Add Font.” Browse to your Downloads folder, click the font you want to install and then click the “Open” button to initiate the automated installation process.
You can use Font Book to manage existing fonts. Font categories are displayed on the left of Font Book. Choose “All Fonts” to view a list of all fonts currently installed on your Mac. To group commonly-used fonts, click “File” on the main menu and choose “New Collection.” Give the collection an identifying name and then drag and drop fonts into the collection.