Learn Croatian: Jabuka je crvena.

In Croatian, adjectives must match the gender of the noun they describe. Because jabuka (apple) is a feminine noun, the adjective takes the feminine ending -a, making it crvena. If we were describing a masculine noun, we would use the masculine form crven.

How do I know that jabuka is a feminine noun?

You can usually guess a noun's gender by its last letter. Most Croatian nouns that end in -a in their base form are feminine. Since jabuka ends in -a, it is feminine and requires feminine adjectives.

Is the word order always like this?

In this case, the order is identical to English because we are stating a fact about the subject: noun (jabuka), verb (je), adjective (crvena). If you wanted to talk about a red apple as a single phrase, the adjective would simply go before the noun: crvena jabuka.

Why isn't there a word for 'the' before jabuka?

Croatian doesn't use articles like 'a', 'an', or 'the'. The word jabuka stands on its own and can mean 'an apple' or 'the apple'. You just rely on the context to know which one makes sense in English.