Learn Croatian: Kruh nije crn. - The bread is not black.

Because adjectives must match the gender of the noun they describe. The word for bread, kruh, is a masculine noun (you can usually tell because it ends in a consonant). Therefore, we use the masculine form of the adjective, crn.

Does crn always mean "black" for any object?

No, only for masculine objects! If you were talking about a feminine noun, like a cat (mačka), you would add an -a to make it crna. For a neuter noun, like wine (vino), you would add an -o to make it crno.

Why is the word for "is not" written as nije instead of ne je?

The verb to be has special negative forms that merge the word for not (ne) with the verb itself. So, instead of combining ne and je, Croatian uses the single word nije.

Where is the word for "The" before kruh?

Croatian does not use articles, which are words like the, a, or an. The single word kruh can mean bread, a bread, or the bread depending on what makes the most sense in the context.