In Spanish there are two ways of saying "you": There's the informal form, tú and the more formal usted (often abbreviated as Ud.)
Whether you use tú or usted depends on a variety of different factors, but it can be a bit intimidating for English speakers used to addressing everybody as "you". Remember the basic difference is how intimate you are with the person.
Here are a few basic rules to help you avoid causing offence or embarrassment:
The form of "you" that you use will change your verb endings. When you're learning your conjugations you'll learn both the formal and informal forms.
See the differences between tú and usted in these examples.
Note: We've included the words tú and usted in the examples above, but it's very common for Spanish speakers to just leave them out. So make sure you pay attention to those verb endings!