How can I use a different size font for the windows I have open? For other applications?

The default font for terminal windows run via the 'xterm' and 'rxvt' programs is set in your ~/.Xdefaults file; the line looks like XTerm*font: 9x15 . Change the 9x15 to the font you want to use. You can change the font for any application in the same way. To pick a font, use the "xfontsel" application. (10x20 is slightly larger than 9x15, and 8x13 is slightly smaller.)

You can also set the font upon startup to most Xwindows applications and terminals (including xterm, rxvt, konsole, gnome-terminal, etc) via arguments to the command, like so: rxvt -fn '-sony-*-*-*-*-*-*-*-*-*-*-*-*-*' Don't forget to put the argument in single quotes (') if it contains shell metacharacters such as asterisks.