Here's a breakdown of the phrase:
* Me da alegría: This literally means "It gives me joy" or "I am happy."
* saber: This means "to know."
* que estás: This is a conjunction "that" followed by the verb "estar" in the present tense. "Estás" can mean "you are" or "you are here" depending on the context.
The meaning is incomplete, as the phrase is missing the object of "estar." You need to add the rest of the sentence to understand the full meaning.
For example:
* Me da alegría saber que estás bien. (It gives me joy to know that you are well.)
* Me da alegría saber que estás aquí. (It gives me joy to know that you are here.)
* Me da alegría saber que estás feliz. (It gives me joy to know that you are happy.)
The phrase expresses a feeling of joy or happiness stemming from the knowledge of someone's well-being or presence.