A basic English sentence needs a subject and a verb.
The subject is the person or thing that does the action, and the verb shows the action or state.
Sometimes we also add an object to show who or what receives the action.
For example:
“Sara reads a book.”
Sara is the subject, reads is the verb, and a book is the object.
Another example:
“The cat sleeps.”
It has only a subject (the cat) and a verb (sleeps), and it’s still a complete sentence.