This is our first ever camping trip. We don't know much except what to bring from the guide. My question is, when we set up camp and decide to go hiking or to the beach or away from our campsite, should we take our tent down or would it be safe to leave it until we return?

Well, campers as a general rule are very honest and friendly folk. I've never worried about my campsite, other than being sure that food was put away to keep it from birds and critters. You will likely never have to take down your tent just to go elsewhere for the day.