Here's a breakdown:
* Olá: Hello (informal)
* Como: How
* Estás: Are you (informal, singular, you)
You can also use "Como está?" if you are addressing someone formally, as "está" is the formal form of "estás".
Example:
"Olá, como estás?" - Hello, how are you? (informal)
"Como está?" - How are you? (formal)