Learn French: Et toi, tu as une télévision ? - And you, do you have a television?

tu is the subject pronoun—it is the one doing the action (tu as = you have). toi is a stress pronoun used for emphasis or after words like et (and). Using both is a very natural French way to say "And you, do you have a television?"

There is no word for "do" in the French sentence. How is this a question?

In conversational French, you can ask a question simply by using the normal statement order (tu as une télévision) and raising your voice at the end, indicated by the question mark. French never uses a helper word like "do" to make questions!

How can I tell that télévision is a feminine word?

The word right before it is une, which is the feminine form of "a". A handy trick for the future: almost all French words that end in -sion or -tion are feminine!