Learn Croatian: Danas smo umorni.

The word for 'we' is mi, but it is dropped here. The verb form smo specifically means 'are' for the 'we' form. In Croatian, you usually leave out the subject pronoun unless you want to emphasize it, because the verb already tells you who the subject is.

Why is smo placed right after Danas? Can I say 'Smo danas umorni'?

No, you cannot start a sentence with smo. It is a clitic, which is a short, unstressed word. Croatian grammar strictly requires clitics to be placed in the second position in a sentence. Therefore, it naturally falls right after the first word, Danas.

Why does umorni end in '-i'?

Adjectives have to match the subject they describe. Since the hidden subject 'we' is plural, the adjective takes a plural ending. The -i ending is used for a group of men, or a mixed group of men and women. If 'we' referred to an all-female group, the sentence would be Danas smo umorne.

I learned that the word for 'tired' is umoran. What happened to the 'a' in umorni?

Croatian has a very common spelling pattern called the 'fleeting a'. When you add an ending to certain words that end in -an, that last 'a' drops out. So, umoran plus the plural -i ending becomes umorni, rather than 'umorani'.