You can go down Groom Lake Road for about 13.8 miles, before you get to the border. It is a well-maintained dirt road, suitable for all cars in decent shape. There are hidden Road Sensors buried in the ground along the road, to give Area 51 security an early warning of approaching vehicles. And of course you are watched from the surveillance installation on Bald Mountain, and by the Cammo Dudes at the end of GL Road.
When you get to the border of the restricted area you will see large warning signs on both sides of the road. You will also see several security cameras and most likely a security vehicle on a nearby hill inside the restricted area. The border itself is marked only by orange posts, spaced about 50 yards apart.
This is the end of the road for most of us. Do not continue past the warning signs. Parking on Groom Lake Road is not advisable, but there is a small dirt parking area on the right, about 1/4 mile before the signs, and some level ground to pull off the road right by the signs.