How is just a command "Go!"? Is it Приготовь?

to go is "Идти" but how imperative mood is formed?

One more кофе-related question: "Go and buy coffee"
"Пойди купи кофе" is the best translation, I think.

"Пошёл!" is more command and sounds like "Are you still here? Go!".
"Пошёл" as a command is ok only addressing a horse or a coachman...
If you say it to a person, it's VERY RUDE (and strange).