As mentioned, a sentence has to be clear in its meaning. If I say "I saw", my meaning is not clear to you. You may want to know what I saw. When I say, "I saw a ghost", I named the thing or object that I saw, and my meaning becomes clear. The word "ghost" is the Direct Object of the verb "saw." The object is the part of the sentence that undergoes the action of the verb, which in this case is saw. The direct object generally comes after the verb. (The verb saw is called a Transitive Verb. A transitive verb needs an object to complete a sentence and make its meaning clear.)

• Some sentences have a subject and a verb. But most sentences have an object. The subject comes before the verb and the object comes after the verb.

EXAMPLE: The dog barks. (subject: dog; verb: barks. No object present.)
EXAMPLE: The dog barks at him. (subject: dog; verb: barks: object: him)

• An object always comes after the verb.

EXAMPLE: A cat catches mice.

• Some verbs are not followed by an object.

EXAMPLE: His train departed at ten o'clock. (No object.)

• Some verbs have two objects – a direct object and an indirect object. An Indirect Object is easily identified by its position in the sentence. It always comes before the direct object. It usually tells us why something is done.

EXAMPLE: He bought her a puppy. (A sentence that contains two/both objects.)
In the example, the indirect object is her and the direct object is a puppy.