The nominal sentence

Arabic has no verb for is in the present: البيت كبير means the house is big. A sentence that starts with a noun is a nominal sentence: a subject (مبتدأ) and a predicate (خبر).

The subject is usually definite and the predicate indefinite: الطقس جميل, the weather is nice. With both definite, it is a phrase, not a sentence: الطقس الجميل means the nice weather.

A pronoun can be the subject: أنا طالب, هي طبيبة, نحن جاهزون. The predicate agrees with it in gender and number.