Hablar is the verb for "to talk".
You say, "How do they know to speak Spanish?"
¿Sabes cómo hablar en inglés?
I want to speak to you I want to talk with you
Please talk in English: Hable por favor en inglés.
I means you don't know how to talk in Spanish What you could say is, No puedo hablar espanol.
"Tu puedes hablar" in English means "You can speak."
"Puedo hablar en inglés" translates to "I can speak in English" in English.
Translation: Puede(s) hablar inglés también. (The (s) is added if you are familiar with the person.)
To talk.
I like to speak spanish... me gusta hablar español
If you meant to say "te hablar" that loosely translates to "you speak" but its not grammatically correct.
You would say "hablar con". For example, "voy a hablar contigo sobre el tiempo", or "I am going to talk to you about the weather."