"Yes, you can just copy the fonts into the /library/fonts, or /users/username/library/fonts... But (!!), that doesn't mean the font is safe...
1) Download the font. 2) Open Font Book 3) Select File --> Validate File, and select the font you downloaded.
Did you receive any error messages regarding the font? If so, just forget about it. It's not worth the effort. Font issues can cause lots of issues in the long run.
If there wasn't an error, close the font, and drag the font to Font book. You'll notice in the lower right hand corner of the Font book preview window is ""Install font"". Click on that button to install the font."