Kanshu, there are 2 forms of "You" in Russian - "Ты" and "Вы". That has an impact on the ends of verbs. "Ты" - less distant, formal and respectful treatment to a person. You can use it for friends, mates, family or children. "Вы" - is plural, it usually used to address to group of people. But also "Вы" - is like plural form for a single person, much more distant, formal and respectful treatment to a person. You should use "Вы" with correct ends of verbs as default to address to an adult stranger, it will indicate that you a person with a good manners. So, "Что делаешь?" - means "Что (ты) делаешь?" "Что делаете?" - "Что (вы) делаете?" P.S. In Russian we have an expression "Перейдем на ты" - it means "From now let's talk in more informal and close way (with another ends of verbs)"