It's a common phrase used in conversation to ask someone about themselves, their thoughts, feelings, or experiences.
Here are some examples of how you could use "et toi":
* "Comment vas-tu?" "Bien, merci, et toi?" (How are you? Fine, thank you, and you?)
* "J'aime beaucoup la musique classique. Et toi?" (I really like classical music. And you?)
* "Je suis allé au cinéma hier. Et toi?" (I went to the cinema yesterday. And you?)