Think of a sentence like a movie: you need a star and you need action. In grammar, those roles are played by the Subject and the Predicate.
Every complete sentence must have both to express a full thought.
1. The Subject (The "Who" or "What")
The subject is the person, place, thing, or idea that is doing or being something. It is usually a noun or a pronoun.
Simple Subject: Just the main noun.
Example: The hungry cat meowed.
Complete Subject: The main noun plus all its descriptive words.
Example: The hungry cat meowed.
2. The Predicate (The "What happened")
The predicate tells us what the subject is doing or what the subject is. It must contain a verb.
Simple Predicate: Just the verb or verb phrase.
Example: The cat meowed.
Complete Predicate: The verb and everything that follows it to complete the thought.
Example: The cat meowed loudly for its dinner.
How they work together
To find them easily, first find the verb (the action), then ask "Who or what is doing this action?"

Sentence	Subject (Who/What)	Predicate (Action/State)
Birds fly.	Birds	fly.
My blue car is in the garage.	My blue car	is in the garage.
Pizza tastes delicious.	Pizza	tastes delicious.
The robot solved the puzzle.	The robot	solved the puzzle.

A Few Tricky Spots
Compound Subjects: When two people share the action. ("John and Sarah went home.")
The "Hidden" Subject: In commands, the subject is often an invisible "You."
Example: "Clean your room!" (The subject is [You], the predicate is clean your room).
Inverted Sentences: Sometimes the predicate comes first.
Example: "Down the hill ran the boy."