Even though the verbs “ser” and “estar” can be translated to the same verb “to be”, there are very different situations in which you can use each.

We use “ser” when something or someone has a permanent characteristic, for example a description. 

We use “estar” to describe a temporary situation. For this reason, when asking someone how they are, we ask “¿Cómo estás?” because we understand that this answer is temporary and can change.