Fact: Not always, but it depends.
Generally speaking, you're expected to complete all of your academic work independently unless your instructor has told you otherwise. Therefore, if you work with others on a class assignment that was intended by the instructor to be an individual assessment, the instructor may consider this academic misconduct.
Always check with the instructor if you aren't sure, and acknowledge the people who helped you on an assignment.
Fact: Copying or using someone else's ideas or words without attribution is always cheating, even if you've paraphrased.
Fact: You cannot use old exams in preparing for or taking a test if it was not explicitly authorized by your instructor. If you come across some old exams for your particular course, ask your instructor if you can use them to study.