As far as I can see there are four different cases. The first three cases concern fonts with direct LaTeX support (there are packages) with different licenses, while the fourth addresses fonts without direct LaTeX support, no matter how they are licensed:
a) Free fonts in the TL repository like
On a well maintained, recent distribution like TL2013 on MacOS it is very likely, that simply updating your system with the TeX Live Utility will install everything needed.
If you don’t have a full installation, just install the package with TeX Live Utility or by running
sudo tlmgr install xcharter in a terminal. (The instructions on font installation, which are often found in the documentation of font packages, are only of import if you are not using a package manager.)
This applies to a whole range of fonts like
gentium to name just a few.
b) Non-free fonts like
There is a number of fonts, including
garamondx, which can be installed using the script
getnonfreefonts. In order to do so, follow the instructions here.
c) Non-free fonts with LaTeX support like
Other popular fonts like
Minion Pro have LaTeX support but need to be installed manually. Usually there are detailed instructions accompanying the packages. In some cases, like Minion Pro, you can even find scripts that do the work for you.
d) Fonts without direct support
There is a huge class of commercial and free fonts without direct LaTeX support. They can be used with fontspec (this option requires XeLaTeX or LuaLaTeX).
More on manual font installation here.
So, to generalize a bit: if a package contains a font and the package is in the TL repository then installing it with a package manager (like
tlmgr) should suffice.
tlmgr) to install
xchartershould suffice and cause no problems.
xchartergets around a bug in