A nominal sentence begins with the subject (noun or pronoun) and not a verb.

.هُوَ من كندا

He is from Canada.
In Arabic, there is no verb “to be” (is, are, …). That is implied in
the rest of the sentence. This sentence has a subject (He) and
predicate (Canada). The predicate may be an adjective or prepositional
phrase, instead of a noun.

.هُوَ ذَكي

He is intelligent.
Here, the subject is “he” and the predicate is “intelligent”.

.أنا في الحديقة

I am in the park.
In this sentence, the subject is “I” and the predicate is “in the park”.