When speaking directly to another person, use the pronoun "you."
How are you today?
I'm fine. How are you?
The word "you" is also used when talking to more than one person:
How are you today?
We're fine. How are you?
Then there's the indefinite form for "you." This is very useful because it can be used in talking about any person or group of people, directly or indirectly:
Smoking is bad for you. (It's bad for any person to smoke.)
You must capitalize the first word in a sentence. (Everyone must do this.)
If you practice English every day, you will improve. (This is good advice for anyone who hears it.)
Here's a video on the use of you as an indefinite pronoun:
One more thing. Remember that "you" is the subject in sentences that are in the imperative form (commands):
Give that to me, please. (The subject in this sentence is "you.")