To understand when to use ser and estar, keep these important points in mind:

1. Who You Are vs. How You Feel:

   • We use ser for things that stay the same. For example, if you say, "Ella es ingeniera," it means "She is an engineer," and that tells us about her identity.
   • On the other hand, we use estar for feelings or situations that can change. For example, "Ella está cansada" means "She is tired" right now.

2. Where Things Are:

   • Use estar when talking about where something is located. For example, "El libro está en la mesa" means "The book is on the table."

3. How We Feel:

   • We use estar to share our emotions. For instance, "Estoy feliz" means "I am happy," and this can change.
   • However, ser describes more permanent traits. Saying "Soy feliz" means "I am a happy person," which tells us more about who you are.

4. Days and Times:

   • Ser is always used when talking about time and dates. For example, "Es martes" means "It's Tuesday."

Try practicing these rules with your own examples, and notice how the words change based on the situation!