Mark the sides of the walkway with a garden hose or rope. Curves and bends in the path can be easily marked in this manner.
Take up sod to a depth of 3 to 4 inches using the blunt-edged shovel within the marked edges of the path. Maintain an even, level depth to prevent rainwater from pooling on the path.
Install metal edging along the entire length of both sides of the walkway according to the manufacturer's directions. Use the rubber mallet to gently pound in bracing clips that come with the edging. The edging will act as a retaining wall for the pea gravel.
Unroll landscape fabric and lay it in place on the path. The fabric should cover the entire width and length of the path to prevent weeds from growing in the walkway. Any overlaps should be 3 to 4 inches to avoid leaving gaps.
Fill the path with pea gravel using a shovel and rake it to fill the walkway to within 1/2 inch of the top of the landscape edging. The pea gravel should be tamped down lightly to pack it into the edges of the path against the edging. This can be done with the back of a rake.
Place the flagstones, starting at one end of the path, approximately an equal distance apart. Using your hands, press and wiggle the stones down into pea gravel, then tap the each stone with a rubber mallet to set it firmly in place. Position the flagstones almost evenly with, not lower than, the pea gravel.