How to tell and use the different "your"?
¿Cómo se llama?
¿Por qué es tu madre vendedora?
Both "se" and "tu" are 'your".
When to use them?
3 Answers
Watch out for the "se" in useages like "¿Cómo se llama?". Although this is normally interpreted as "what is your name", that is not the litteral translation, which is "what do you call yourself". The "se" is a reflexive pronoun in this case.
The two pronouns you seek are "tu" for informal situations, and "su" for formal. Be aware that "su" can also be their, his, hers, or its. "Este es su libro". Could be "This is your book" or "...his book" or "..her book" or "...their book". You need context to know which one is implied.
"Tu" always means "your". In the singular informal sense. Again, for the plural "you", (ustedes), it would be "su", or in Spain perhaps "vuestra".
You use te, tu, informally, talking to your friends, common people. Cómo te llamas? Cuál es tu nombre? What's your name? (TÚ)
You use se, su formally when talking to adults, elders, people in higher positions etc. Cómo se llama? Cuál es su nombre? (USTED)
¿ Cómo te llamas ? What's your name = familiar.
¿Cómo se llama? Whats you name ? = formal