The two main parts of every sentence and every clause are subject and predicate.
The subject is what a speaker is talking about.
The main word in the subject will be a noun or a pronoun.
This main word is the SIMPLE SUBJECT.
The subject word with all the words that describe it is called the COMPLETE SUBJECT
The subject may be a single word:
Cats are beautiful. (simple subject)
He won the lottery. (simple subject)
The subject may contain several words:
The tall, red tower stood beside the sea. (complete subject) The simple subject in this sentence is tower.
The subject may contain phrases as well as single words:
That good-looking boy in the blue shirt watches out for the younger children on the playground. (complete subject) The simple subject is boy.
The subject of a sentence usually comes before the predicate, but sometimes it comes after it. When the subject comes after the predicate, it is called a delayed subject. Here are some examples:
There were three kittens on the porch. (complete subject)
Once upon a time lived a horse with wings. (complete subject)
Delayed subjects are explained in more detail elsewhere on the site.