If you have a .ttf file (lets call it your_font.ttf) that you have downloaded and want to install it as an available font you should follow these steps:
1. Create somewhere to keep your .ttf fonts:
sudo mkdir /usr/share/fonts/truetype/custom
2. Copy your font there:
sudo cp your_font.ttf /usr/share/fonts/truetype/custom
3. Run the following command to rebuild your font cache:
sudo fc-cache -f -v
That should be it! Your sexy new font should now be available.
