Fonts are handled by the respective global system control panel. Nothing specific Adobe, so check there.
As Mylenium said, installing fonts is a global function relating to your OS. It has nothing to do with After Effects - After Effects uses fonts that are installed into your OS.
What Andrew and Mylenium say is true, but here's some more information, from "Fonts":
"In addition to the fonts installed on your system in the standard location for your operating system, After Effects uses font files in this local folder:
Program Files\Common Files\Adobe\Fonts
If you install a Type 1, TrueType, OpenType®, or CID font into the local Fonts folder, the font appears in Adobe applications only."
On Windows, you can install the fonts here: C:\Windows\fonts\
Note that you will need the administrator rights to modify the content of that folder.
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