How can I determine which fonts are installed from the command line, and what is the easiest way to install more?

The best and simplest way is to use console command (this command should be available for all ubuntu-based distributions) :

fc-list

Example output (stripped) :

/usr/share/fonts/truetype/lato/Lato-Medium.ttf: Lato,Lato Medium:style=Medium,Regular
/usr/share/fonts/truetype/tlwg/TlwgTypo-Bold.ttf: Tlwg Typo:style=Bold
/usr/share/fonts/truetype/lato/Lato-SemiboldItalic.ttf: Lato,Lato Semibold:style=Semibold Italic,Italic
/usr/share/fonts/truetype/dejavu/DejaVuSerif-Bold.ttf: DejaVu Serif:style=Bold
/usr/share/fonts/truetype/noto/NotoSansThai-Regular.ttf: Noto Sans Thai:style=Regular
...

From MAN :

fc-list - list available fonts

To check all available options use MAN (manual): man fc-list

What version of Ubuntu are you using?

(1) Thanks to the links from Lety, on my ubuntu 15.04 machine less /etc/fonts/fonts.conf. In there it describes how to use local.conf.

(2) from a command line, to search for more fonts I use apt-cache search font | grep lcd then I use apt-cache show {} (replacing {} with the package name) for a more detailed description. installation from the command line has several variants (like aptitude) but good old sudo apt-get install {} works well.

Answer for 2nd question:

Installing font is just copying its file to some folder. There can be many folders. At my system they are:

• /usr/share/fonts/ — fonts for all users
• ~/.local/share/fonts/ - fonts for particular user

There can be any subfolders you want.

Here is the command to get list of font files that your system uses.

fc-list -f '%{file}\n' | sort

Look at it and you'll get the idea of where fonts in your system located/