Retaining walls serve lots of decorative and functional purposes in any garden. For instance, if you have a kind of steep part on your property that you would like to see level, or if you would like a small area of your property set apart as a decorative garden, a concrete block retaining wall should be exactly what you need to achieve that. Taking these individual blocks of beautifully molded concrete and create a wall with them might seem to the novice like a kind of complicated project. You would find though that at any DIY building supplies store, they have blocks specifically manufactured and finished for the first time do-it-yourselfer.
The first thing you need to know about building a block retaining wall in your garden is that these blocks are shaped and grooved to just lock into place. You don't need any water or any special retaining mechanism. It can be rather fun putting them together kind of like the Lego blocks you probably played with as a child, only bigger and heavier. It can be difficult to make a mistake with these. You just have to slide them out and they'll be ready to go anywhere else you put them.
Mostly, since a block retaining wall uses no mortar or other binder, they'll be safer in low-rise designs no higher than 2 feet or so. The way the grooves in the blocks are shaped, they don't fit together in a stiff and flexible manner. You can easily wiggle them about even once you've set them together. What that means is, you can easily set blocks together to form a curved wall.
The actual process of building a block retaining wall couldn't be simpler. Your first step would be to trace out in the soil the exact shape the wall is to be. You can mark the route the wall is to take with a garden hose or something. Once you've done that, you need to dig out a trench to settle the base course of the wall into. Most blocks happen to be 4 inches deep. You could dig a trench 5 inches deep and as wide as the blocks are, tamp the soil down and add a layer of leveling sand about an inch deep.
Now that you have of a proper foundation for your blocks, all you need is to begin laying them. Since the foundation course is on somewhat uneven ground, you need to check the level on each stone you lay, tamping and adjusting to make everything lie flat. Once the entire initial course is laid, you can use a line level to make sure that the entire course is the exact same level. If you wish to lay your stones in a staggered fashion for extra strength, you want to cut the first and the last blocks in half with a hammer and chisel. When you finish laying the first and second courses, you could make sure that soil doesn't fall into the spaces between the blocks by covering the cavity behind the wall with landscape covering fabric.