Learn Croatian: Ovaj grad je velik.

Ovaj means this, and we use it because the word it points to, grad (city), is a masculine noun. If the noun were feminine, we would use ova, and if it were neuter, we would use ovo.

How do I know that grad is a masculine noun?

In Croatian, you can almost always guess a noun's gender by its last letter. Because grad ends in a consonant (the letter d), it is a masculine noun. Feminine nouns typically end in a, and neuter nouns usually end in o or e.

Why is the word for big spelled velik here instead of veliki?

Both words mean big, but velik is the short form. We use the short form here because it comes after the verb je to describe the subject. If we put the adjective right in front of the noun (like saying the big city), we would use the long form veliki grad.

Could I say ovaj je grad velik instead?

Yes, you can! The little word je is a clitic, meaning it naturally wants to be the second word or phrase in a sentence. Treating ovaj grad as one block makes je the second piece, but putting it right after ovaj is also very common and sounds natural.