For moods and feelings Italian uses essere: sono contento, è stressata. Stare is reserved for how you are keeping - sto bene, sta male. Either way the adjective agrees: contento, contenta, contenti, contente.
Examples
- Oggi sono stanca.
- Today I am tired.
- Come stai? Sto bene, grazie.
- How are you? I am well, thank you.
- I ragazzi sono contenti del risultato.
- The boys are happy with the result.
The mistake to avoid
Sono bene is wrong for how you are - that one needs sto bene.
Where this fits in
Body, health & feelings, Italian A2: Talk about your body, common illnesses, and how you feel. Visit a doctor or pharmacy and describe symptoms.