Demarcate the area of your lawn you want to edge. Spread a thin layer of powdered chalk or stretch out a garden hose to define curved areas. Boards can be used to define straight lines. Measure the length to determine how much edging material you need. Steel edging usually comes in 10-foot lengths.
Dig a 4- to 6-inch trench along the marked lines with a shovel. Keep it as wide as the edging material. Collect the dirt in a wheelbarrow and set aside for other gardening projects, or discard appropriately. Level the base of the trench with a length of 2-by-4 so it is even.
Position a length of steel edging upright in the trench, starting at a corner. Bend it to follow any curves, if necessary. Check that the stakes attached with the trench fall inside the lawn.
Push the edging down into the trench until one-half-inch of the rounded top is visible above the surrounding ground level. To cut any excess edging off, mark a deep vertical cut over the section with a hacksaw and bend it back and forth until it snaps into two pieces.
Hammer the stakes down so they penetrate the ground to hold the edging in place. Commercial steel edging material features stake pockets with stakes at every two feet.
Inspect the edging after installation. Add dirt into any gaps between the edging and the trench. Lightly sprinkle the soil around the edging with a garden hose so it settles down and holds the edging better.