What is predicate (subject you understood)?

The predicate is everything that is not the subject. The simple predicate is a verb or verb phrase. eg

The man next door is a doctor

complete subject = The man next door, complete predicate = is a doctor.

simple subject = man, simple predicate = is

The woman is waiting for her husband.

complete subject = The woman, complete predicate = is waiting for her husband.

simple subject = woman, simple predicate = is waiting