The subject of a verb is the person, animal or thing that does the action.
The horse ate the apple.
In this sentence, the horse was doing the eating, so it is the subject.
The object of a verb is the person, animal or thing that receives the action.
The horse ate the apple.
The apple is the object because it was being eaten.
Every sentence must have a subject, but not all sentences need an object.
The horse neighed.
The horse is the subject of the sentence, but nobody is being neighed, so there is no object.
Let's move on to the questions now.