Learn Arabic (Modern Standard): هذا رجل ذكي.

In Arabic, simple equational sentences in the present tense do not use a verb for "is" or "are". Placing the subject هذا (this) right before the predicate رجل (man) naturally creates the meaning "This is a man".

Why does the adjective ذكي (smart) come after رجل (man)?

In Arabic, adjectives always come directly after the noun they describe. So instead of saying "smart man", the word order is literally "man smart".

How do the noun and adjective match each other here?

Adjectives in Arabic must agree with their nouns in gender and definiteness (whether they have "the" or not). Since رجل is a masculine noun without the definite article ال (the), the adjective ذكي must also be masculine and without ال. This perfect match creates the phrase "a smart man".

How do we know this means "This is a smart man" and not just the phrase "This smart man"?

When the word هذا (this) is followed by an indefinite noun (a noun without ال), it forms a complete sentence meaning "This is a...". If you wanted to say the fragment "This smart man", you would need to make both the noun and adjective definite by adding ال to them: هذا الرجل الذكي.