tener
Tener means 'to have' — but Spanish uses it where English says 'to be', making a whole class of sentences feel backwards.
tener (have)
Possession — physical, abstract, and relational. Standard 'to have.'
Tengo tres hermanos.
I have three siblings.
Straightforward possession. No surprises here.
Tiene mucho talento.
She has a lot of talent.
Abstract possession. Also normal.
Tengo que irme.
I have to go.
Tener que + infinitive = have to. The workhorse of obligation in Spanish.
tener (to be)
Used where English says 'to be' — for age, hunger, thirst, heat, cold, fear, luck, and more. These must be memorised.
Tengo hambre / sed / frío / calor / sueño / miedo.
I'm hungry / thirsty / cold / hot / sleepy / scared.
All of these use tener in Spanish, not ser or estar. 'Estoy hambriento' exists but is less common; 'soy hambre' is wrong.
¿Cuántos años tienes?
How old are you?
Age uses tener, not ser. 'Tengo treinta años' = I am thirty. Never 'soy treinta años.'
Tienes razón.
You're right.
'Tener razón' = to be right. Fixed phrase. 'Estás correcto' works too but 'tener razón' is more natural.
Tricky bit
The tener expressions (hambre, sed, miedo, razón, suerte, prisa) are non-negotiable fixed phrases. Don't try to logic your way to them — just learn the list. 'Estoy con hambre' is heard in some regions but 'tengo hambre' is universal.