With an adjective, ser describes what someone is like as a person and estar describes how they are right now. Es nervioso means he is a nervous type; está nervioso means he is feeling nervous today. Feelings almost always take estar.
Examples
- Hoy estoy cansada, pero normalmente tengo energía.
- Today I am tired, but I usually have energy.
- Es una persona tranquila.
- She is a calm person.
- Está muy contento con el trabajo nuevo.
- He is very happy with the new job.
The mistake to avoid
Es aburrido means he is boring; está aburrido means he is bored.
Where this fits in
Body, health & feelings, Spanish A2: Talk about your body, common illnesses, and how you feel. Visit a doctor or pharmacy and describe symptoms.