How do I install a plain text font onto a mac? I m trying to use this one: http://scripts.sil.org/cms/scripts/page.php?site_id=nrsi&id=OFL
The main website, sil.org, is for "Summer Institute of Linguistics". They provide many fonts. Find the one you want at their downloads page, linked below.
I DO NOT suggest that you double-click a font to use Font Book to install, unless you change the preferences for Font Book first. Font Book has a default preference to install fonts into your personal home directory. That will make the fonts unavailable to any other user. The only reason to have "private" fonts is if you deal with a limited number of fonts in a group of publishing workers. Even then, it rarely is needed. This is one aspect of OS X that needs changing, along with having the firewall off by default.
The simple method of installing fonts for universal use is to use a Finder window (maybe two windows) to just drag the font to the location
There are 3 locations for Fonts in Mac OS X:
/System/Library/Fonts (for fonts installed by Apple – DO NOT GO HERE)
/Users/your home folder/Library/Fonts (for private fonts available ONLY to that one user)
/Library/Fonts (for fonts available to any user)
Right now, you may be the only user, so it seems inconsequential, but later you may add a second or third user, and if the new users can't use your fonts, they will be confused.
MORE FREE ADVICE (and worth every penny)….
Although the SIL website is trustworthy, as general rule is to be very cautious of any software that is archived as ZIP. The usual archive for Mac software is DMG. The difference is that a ZIP can be programmed to self-expand and the contents may self-install. A DMG archive does not have that "feature".
First off that link is to a license, not to any particular font description. Once you find the download page for the font you want, download the .zip version and extract the .ttf or .otf file from that. Then look at:
…and scroll down to the Mac instructions. Apparently you just double-click the font file to get a preview, and then click a button from there to install. You may have to extract the ttf/otf file from the .zip archive first.
You select the font you want and click the download button…
Double click the zip file to unzip it
Double click the folder to open it
Double click the .ttf file which will open the Mac's Font Book app
Click the Install Font button
You linked us to a license, not a font. A font should be a *.ttf file, or *.woff, or what have you.