Spray paint the path's edges on the grass. Be as precise as possible. Use a tape measure to mark the width every 2 feet along the path, then connect those marks. If you do not want to use spray paint, garden hoses or laundry lines work just as well.
Mark the path's entire outline with a shovel, pushing the tip approximately 3 to 4 inches into the ground. Once the outline is marked in the dirt, angle the shovel towards the path and remove the sod and dirt within the outline. Dig the path approximately 4 inches deep, keeping it as level as possible.
Tamp the path down with either a hand tamper or a plate compactor. Be sure the path is level by placing a level across the path in various locations. Add dirt to any low areas and tamp it down.
Install metal garden edging along the path's sides. Most metal edging has hooks on the backside. Hammer the supplied metal stakes through the hooks to hold the edging in place. If your metal edging has no hooks, hammer a metal stake along the path's sides every 2 to 3 feet for the edging to press against. Push the edging tight against the stakes and hammer it into the ground until it is about 1/2-inch above ground level.
Lay a strip of filter fabric along the path. Use scissors to cut the fabric to fit in the path. Pour pea stone or stone dust onto the filter fabric. Use a metal rake to evenly spread a 2-inch layer over the filter fabric.
Look at both sides of the stone and determine which is the smoothest. Lay the stone on the pea stone or stone dust with the smoothest side up. Push down on the stone and wiggle it around a bit so it's positioned securely. Place a level on the stone. Tap the higher corners with a rubber hammer until the stone is sitting straight.
Lay the remaining stones the same way. The distance between each stone is up to you. Flagstones are not perfectly formed. They are different sizes, shapes and widths. Some people like to place the stones close together while other people keep them a few inches apart.