Answer:
Ser is for describing WHAT something is and estár is for describing HOW something is
Explanation:
When you are describing how you feel to another person, you use estár.
Example: Estámos contentos pero muy cansados - We're happy but very tired
However, when you are describing WHAT something is you use ser
Example: Son las ocho y media de la mañana - It's eight-thirty in the morning
Something that might help you remember this
When describing how you feel and where you are always use the verb estár
