Marshrutka is a jitney-like mode of transport that falls between private transport and conventional buses. The role of the modern Russian marshrutka is basically similar to the minibus in other countries. It is similar to German Sammeltaxis, Mexican Peseros and American dollar vans. Trip costs can be different, depending on marshrutka line. Usually one trip costs 25 rubles. You give money to the driver just having entered the minibus. If you need to take it off, you have to cry: "Остановите здесь!" (Ostanovite zdes, means "Stop here!"). You should shout it as loudly as it is possible, because the motor roar and the music sounding from the driver’s audio system muffle the passengers' voices. Sometimes the marsrutkers hang out an inscription: "Тише скажешь – дальше выйдешь", meaning the more silently you cry, the farther you leave the Marshrutka.
You should cry it in Russian, because the Marshrutka drivers speak no other language and even the Russian they speak very bad.
Generally marshrutkas go a little faster than buses: however they may be operated by reckless drivers and thus become dangerous. Unless you're in a hurry, more convenient buses/trolleys/trams are a safer option.