Most human languages have separate words for you-singular and you-plural. Russian is no exception. The plural you in Russian is вы, which declines like this:

Any time you address more than one person in Russian, you must use the вы form instead of the ты form:

In Russian the вы form is also used to speak politely to a single individual; it's the form you normally use when meeting a stranger or talking to someone who is your superior at work or to someone you don't know very well:

Now here is a subtlety. If вы is the subject of a sentence that has a predicate adjective, and if the adjective is a short form adjective, then you must use the plural form; but if it is a long form adjective, you must use the singular with corresponding gender agreement. Thus if I am talking to a woman I may say:

If I am talking to a man, I may say:

I should note that some of those sentences may sound a bit stilted in Russian. Russian-speakers tend to use predicate adjectives less often than English-speakers, and one needs a bit of experience to figure out when they sound okay and when one should use an alternative constructive. Grammatically, though, all four sentences are correct.