There is a parking lot available to park, which does charge a fee, but there is not admittance fee.
You may walk the paths for free or buy a ticket for a trolly ride.
What to see: the magnitude of graves, Robert E. Lee's home, The Kennedy's graves, The Tomb of the Unknown Soldier, Iwo Jima (outside the grounds, a 15 min walk).
Robert E Lee's home has tourguides inside who offer insight to Lee's family. You walk through on your own and these tourguides are placed throughout the house. You could spend 15-30 min here at the house.
John F. and Jackie's gravesites are set aside from the other other gravesites. Signs are posted to be respectful and quite around the graves. My son was calling me and I answered only to tell him I couldn't talk. The guard quickly told me I needed to get off the phone.
At the Tomb of the Unknown soldier you can see the changing of the guards if you time it right. I'm not sure how often they change. We got there at the tail end of it. You might want to do further research to find out how often they change. That would have been interesting to see.
As you are walking back to the entrance, go out the front gates and walk about 15 minutes to Iwo Jima. This monument is outside the cemetary grounds and there are no signs. You will get directions from the information desk but these directions don't tell you where to go once you are out of the grounds. Keep walking toward the large bell tower (which was a gift from Holland to the US) and you will begin to see the monument. At the top of the hour, the bell tower plays the Star Spangled Banner. That gave me chills. Time it so you can hear this. Record it on your phone so you can share this with your family or students back home.
We spent about 3 hours here. When we left the cemetary, we drove a very short distance across the bridge and found parking to visit Lincoln Memorial, The Vietnam Memorial, and the World War II Memorial. These momuments are all on the same large piece of land and are within walking distance from each other. As a matter of fact, we walked from here to see the White House. It was several blocks away but very doable. Parking along the street is limited to 3 hours.