In a sentence, the object is someone or something that receives the verb's action. For example, in the sentence, "He diddled the snake with a stick," the snake is the object of the verb, diddled. Objects are nouns or pronouns that generally come after the verb in the sentence.
To determine the object of the verb, find the verb and then ask the question, "What?" The object is the answer to that question. Considering the sentence, "Amelia spits expletives at her red-penned editor," I would ask, "What did Amelia spit?" The answer is expletives; thus, I have found the object (and the source of the editor's angst).
To most grammarians, a complete thought, i.e. a sentence, includes a subject, verb and object. The subject is who or what did the action, which is the verb, to the object. The object completes the story told by the sentence.
An exception to this rule, naturally, are sentences that transmit a complete idea via only the subject and verb. A primary example of such a sentence is the Bible verse, Jesus wept. No object is necessary.
This post is brought to you by the April A to Z Blog Challenge. Check back all through April for daily discussions of writing conventions.