When you are talking to someone you need to respect, you should change the pronouns that you use. Instead of using tú, which is the informal way to address the second person, you should use Usted.
For most cases, this changes the conjugations of the verbs that you use. Typically, the subject of the sentence is implied in Spanish, but this is not the case when you use Usted. You have to add the pronoun in order to avoid confusion with the third person singular, since the two subjects share the same verb conjugations. For example:
- ¿Cómo está Usted?
- How are you?
- ¿Cómo puedo ayudar a Usted?
- How can I help you?
