Here are some ways to respond, depending on the situation:
If you have a specific class:
* Tengo [nombre de la clase]. (I have [class name].)
* Tengo [nombre de la clase] con [nombre del profesor]. (I have [class name] with [teacher's name].)
* Tengo [nombre de la clase] a las [hora]. (I have [class name] at [time].)
If you don't have class:
* No tengo clase. (I don't have class.)
* Tengo libre. (I have free period.)
To ask back:
* ¿Y tú? (And you?)
* ¿Qué clase tienes? (What class do you have?)
Formal vs. Informal:
* If you're speaking to someone you know well, you can use informal language like "Tengo" (I have).
* If you're speaking to someone you don't know well or in a formal setting, use formal language like "Yo tengo" (I have).
Example responses:
* Tengo español. (I have Spanish.)
* Tengo matemáticas con el señor López. (I have math with Mr. Lopez.)
* Tengo física a las 8:00. (I have physics at 8:00.)
* No tengo clase. Tengo libre. (I don't have class. I have free period.)
* ¿Y tú? ¿Qué clase tienes? (And you? What class do you have?)