Where do you want the wall?

Finding the correct spot for the wall is a important factor.

In front of the house
Along the driveway
Off the back patio or porch
Steep cliffs to retain soil erosion
Lining the sidewalk
Just for appearance of the house
Cut into a hillside
Tree ring- for trees or couple flowers

Retaining walls are a great way to create a more useful, beautiful, and sometimes safer landscape around your home Lets say your back door opens right up to a steep hill, robbing you of level area for a patio, build a single, tall retaining wall across the yard a distance from the house and level the terrain between the house and the wall. Maybe a terraced landscape at different levels for plantings and gardens. Depending on the scale of the project, you may be able to make the cuts into the hillside and redistribute the soil behind the wall, or you may need a machine. Maybe rent an easy-to-operate mini-backhoe/loader; otherwise, hire an excavator. While nothing can really match the beauty of a finely crafted stone wall, building one is harder than the skill of most homeowners and even masons. However, the average do-it-yourselfer can easily build a retaining wall system using concrete masonry units instead of stone. Concrete and masonry supply outlets stock a variety of styles, but most brands have a rough "stone-like" texture on the face and are designed either to interlock or to be pinned together.

In the picture above the walls above 3 feet should be geogrid, which he is standing on.
Every 3 or 4 rows the geogrid is placed and the locking backsets will stop it from moving.
Then you backfill the wall up to a foot or 1.5 feet away with the soil the the rest of the
backside of the wall to the soil with crushed limestone and tamp away till packed about
2 to 4 times pass over it.

Remember the tamper can only can pack about 3 to 5 inches at a time of soil or the wall will collapse after the first rain or freezing weather.