what does it mean to "dare del lei" to somebody?

In Italian when you have to show respect to a person (somebody you don't know, an older person, a colleague, a teacher... basically everybody who's not a friend) you don't address him a "tu" (you) but as "lei" (third person female pronoun), and therefore you have to decline verbs, pronouns and adjectvies accordingly.

For example if you were to ask a stranger "excuse me, can you tell me where the bus stop is?" you wouldn't say " scusa, mi puoi dire dov'è la fermata del bus" but " mi scusi, mi può dire dov'è la fermata del bus".