Who are you talking to? tú vs. Ud

There is a difference between tú? and Ud.? When you are talking to your amigos (friends), or just somebody your age or younger you ask a question with tu? but when you are talking to somebody superior you say Ud.? to show respect. 

tú is for friends
usted shows respect

 Click HERE and HERE  to see videos of a student talking to their best friend vs. talking to a grown up.