Stretch a garden hose across your landscape to map out the direction of your pathway. The hose will represent the width and length of your path. You can also use marking paint or wooden stakes and cord to map this out.
Trace the outside edge of your hose with the end of a sharp hoe or shovel to create a line in the ground that maps out your pathway. Dig the shovel or hoe as far into the dirt as you can, cutting through small tree roots if necessary. Continue until you have traced out your entire pathway.
Remove the hose. Excavated the traced out area to a depth of 3 to 4 inches to allow room for the foundation of your walkway.
Line the sides of the excavated pathway area with steel edging, which will hold the pathway foundation and stones in place. Press the edging firmly up against the sides of the trench and tap the provided spikes into place with a hammer or mallet to hold everything secure.
Cover the bottom of the excavated area with filter fabric, also known as landscape fabric. The fabric will stop roots or weeds from growing up under your flagstones, and will also help rainwater drain away into the soil instead of sitting in your pathway.
Spread a 1- to 2-inch layer of keystone or gravel over the filter fabric. Use a garden hoe or rake to spread this out evenly over the surface; make sure it does not run over the sides of the edging. This material will support the flagstones.
Set your first flagstone on top of the keystone material, nearest any other walkways or driveways that lead up to the pathway. Lay all stones flattest side up, so that chips and divots are hidden underneath.
Wiggle the flagstone back and forth a few times so that it displaces some of the underlying keystone and settles into the material. Tap it into place with a rubber mallet until it sits flush with the walkway or driveway; if the stone sits up higher than the adjoining walk, it may cause someone to trip.
Set all remaining flagstones in the path, spacing each 6 to 8 inches apart as you prefer for the proper stepping space. Use the rubber mallet to make sure each embeds firmly into the underlying keystone.