Russian uses pronouns in much the same way English does; they take the place of, or refer back to nouns. The table below shows the correspondence between Russian and English pronouns:
я | I |
ты | you (sing, and informal) |
он/она/оно | he/she/it |
мы | we |
вы | you (pi. and formal) |
они | they |
As you can see by this table, Russian has two pronouns for the second person you. Ты is informal and singular; вы is formal and/or plural. (See the comments on ты andвы in Lesson 3).
As in English, Russian pronouns change form as their function changes in the sentence. Take a look at the following sentences:
I know you.
You know me.
I changes to me when it switches from the role of subject to the role of object.
Я знаю вас.
Вы знаете меня.