This is the 39th most frequent Croatian word.
kaže
"Kaže" means "says" in English.
'Kaže' is used impersonally here, acting as 'it is said', to express a general statement or proverb.
Kaže se da je bolje spriječiti nego liječiti.
It is said that it's better to prevent than to cure.
The word 'kaže' is used here as the verb 'to say' in the 3rd person singular (he/she/it says). It introduces a reported speech or statement.
On kaže da će doći sutra.
He says that he will come tomorrow.
Again, 'kaže' is the verb 'to say,' used here to indicate direct speech directed towards the first person with the pronoun 'mi' (to me).