Terminal emulator
vt(1) is the terminal emulator for Plan 9, it's main use case is for programs such as telnet(1) and ssh(1) where they usually expect a form of terminal emulator existing. You don't need vt to run plan 9 programs!
1 connecting to unix systems
The argument -r sets vt(1) in raw mode, which is required by most, if not all programs of UNIX. Raw mode allows the program handle details of screen and keyboard shortcuts (such as, ctrl-a or tab for example) instead of the terminal. You may also set the emulated terminal type using -a, -2 and -x which set the emulated terminal to ASCII, VT220 and XTerm respectively. by default VT100 is emulated, which have no colors, use XTerm if you want colors. Default background color is white (what else?), but if you enjoy black, pass -b
2 fonts
Like all plan 9 programs, vt(1) too uses bitmap fonts, you may set it with -f argument. for example, for nice large fonts:
; vt -rxbf /lib/font/lucidasans/typeunicode.16.font ssh username@domain.com