Begin by preparing the site. Remove sod, weeds, plants, etc. along the path route. Mark the path perimeters with outdoor marking paint. Visit your local landscape supply facility and choose the flagstone for your path. The flagstones should have a level surface and be large enough to accommodate foot traffic, but not so large to be difficult to handle.
Excavate approximately 4"; the actual path depth will depend upon the thickness of the flagstones. Many people like to place landscape fabric at the bottom of the path, but I've found that it tends to hold water too long when it rains, then the path becomes "mushy" when you walk on it. Edging is optional.
Add approximately 3" of 1/4" minus crushed gravel to bottom of excavated path. Rake until smooth and level, then use a hand or machine tamper to compact and level the gravel.
Set the flagstones onto the gravel at a comfortable distance for walking from stone to stone. Seat in the crushed gravel by wriggling them back and forth until they are firmly embedded in the gravel. You may have to scoop away or add gravel below each flagstone to get them level with the ground surface.
Finish by filling cracks between flagstones with blended soil. You can add groundcovers between each stepping stone if desired. Enjoy your new path!