I used my grandfather's auger-type post hole digger, but a shovel or other post hole digger will work. You just need a hole about 18 inches deep and a foot in diameter. Of course, the type of ground makes a difference. Doing this in soft beach sand might be disastrous. Rocky soil could make a solid foundation by very hard to dig. Clay is best.
Once we get the holes dug, we will fill the area around the 4x4's with 50 lbs of concrete each for a solid foundation