If you submit as your own work an essay containing without acknowledgment material which is not your own, then you have committed plagiarism.
Plagiarism is dishonest and unfair to other students.
It is also an intellectually useless activity. Learning to think involves making an effort to articulate and think through ideas and issues yourself. Your written work gives you a chance to come to terms with complex issues and get some feedback on your efforts. Give full references to the sources. If you paraphrase material from any source, again full references must be given.