Jokin - something Joku - someone Joka - it can mean different things like 'who', 'that', 'which' and 'every' depending on how it's used. For example, "Medvedev, who is the president of Russia, declined to comment." = "Medvedev, joka on Venäjän presidentti, kieltäytyi kommentoimasta." Silly example :P "Menimme lenkille, joka/mikä oli mukavaa." = "We went for a jog, which was nice." "Nukun vähintään kymmenen tuntia joka päivä." = "I sleep at least 10 hours every day."