How do you get to the Grand Canyon from Las Vegas or Hoover Dam?

My husband and I are going to LV this week and we are woing to take a day just to drive around and see things that we have never seen, or may never see again. We are going to go to Hoover Dam and then from there we want to get to the Grand Canyon. Just somewhere that we can park and look at the greatness, we are not wanting to go into the canyon, we we do, but don't think we will have the time. I will make the umption that there are signs on the highway, so general directions should be fine. Thanks....