A simple sentence is a basic statement containing a subject and a verb. The subject is the person or thing doing something. The verb is the action that is being done.
Look at these simple sentences. In each sentence, somebody or something is doing an action.
Bob rode his bike.
The dog ran fast.
Mom is baking a cake.
School starts tomorrow.
To write a simple sentence, you must have somebody or something doing an action.
It’s your turn. Write a simple sentence. Be sure to begin the sentence with a subject and then use a verb to show what action the subject is doing.